Systems and methods for controlling reactivity in a nuclear fission reactor

ABSTRACT

Illustrative embodiments provide a reactivity control assembly for a nuclear fission reactor, a reactivity control system for a nuclear fission reactor having a fast neutron spectrum, a nuclear fission traveling wave reactor having a fast neutron spectrum, a method of controlling reactivity in a nuclear fission reactor having a fast neutron spectrum, methods of operating a nuclear fission traveling wave reactor having a fast neutron spectrum, a system for controlling reactivity in a nuclear fission reactor having a fast neutron spectrum, a method of determining an application of a controllably movable rod, a system for determining an application of a controllably movable rod, and a computer program product for determining an application of a controllably movable rod.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to and claims the benefit of theearliest available effective filing date(s) from the following listedapplication(s) (the “Related Applications”) (e.g., claims earliestavailable priority dates for other than provisional patent applicationsor claims benefits under 35 USC §119(e) for provisional patentapplications, for any and all parent, grandparent, great-grandparent,etc. applications of the Related Application(s)). All subject matter ofthe Related Applications and of any and all parent, grandparent,great-grandparent, etc. applications of the Related Applications isincorporated herein by reference to the extent such subject matter isnot inconsistent herewith.

Related Applications

For purposes of the USPTO extra-statutory requirements, the presentapplication constitutes a continuation-in-part of U.S. patentapplication Ser. No. 12/590,447, entitled SYSTEMS AND METHODS FORCONTROLLING REACTIVITY IN A NUCLEAR FISSION REACTOR, naming Charles E.Ahlfeld, Ehud Greenspan, Roderick A. Hyde, Nathan P. Myhrvold, Joshua C.Walter, Kevan D. Weaver, Thomas Allan Weaver, Lowell L. Wood, Jr., andGeorge B. Zimmerman as inventors, filed Nov. 6, 2009 now U.S. Pat. No.9,190,177,

The United States Patent Office (USPTO) has published a notice to theeffect that the USPTO's computer programs require that patent applicantsreference both a serial number and indicate whether an application is acontinuation or continuation-in-part. Stephen G. Kunin, Benefit ofPrior-Filed Application, USPTO Official Gazette Mar. 18, 2003, availableat http://www. uspto.gov/web/offices/com/sol/og/2003/week11/patbene.htm. The present Applicant Entity (hereinafter “Applicant”)has provided above a specific reference to the application(s) from whichpriority is being claimed as recited by statute. Applicant understandsthat the statute is unambiguous in its specific reference language anddoes not require either a serial number or any characterization, such as“continuation” or “continuation-in-part,” for claiming priority to U.S.patent applications. Notwithstanding the foregoing, Applicantunderstands that the USPTO's computer programs have certain data entryrequirements, and hence Applicant is designating the present applicationas a continuation-in-part of its parent applications as set forth above,but expressly points out that such designations are not to be construedin any way as any type of commentary and/or admission as to whether ornot the present application contains any new matter in addition to thematter of its parent application(s).

BACKGROUND

The present application is related to controlling reactivity in anuclear fission reactor.

SUMMARY

Illustrative embodiments provide a reactivity control assembly for anuclear fission reactor, a reactivity control system for a nuclearfission reactor having a fast neutron spectrum, a nuclear fissiontraveling wave reactor having a fast neutron spectrum, a method ofcontrolling reactivity in a nuclear fission reactor having a fastneutron spectrum, methods of operating a nuclear fission traveling wavereactor having a fast neutron spectrum, a system for controllingreactivity in a nuclear fission reactor having a fast neutron spectrum,a method of determining an application of a controllably movable rod, asystem for determining an application of a controllably movable rod, anda computer program product for determining an application of acontrollably movable rod.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A-1U are illustrations in partial schematic form of illustrativereactivity control assemblies for a nuclear fission reactor.

FIGS. 2A-2AP are illustrations in partial schematic form of illustrativereactivity control systems for a nuclear fission reactor having a fastneutron spectrum.

FIG. 3 is an illustration in partial schematic form of an illustrativenuclear fission traveling wave reactor having a fast neutron spectrum.

FIG. 4A is a flowchart of an illustrative method of controllingreactivity in a nuclear fission reactor having a fast neutron spectrum.

FIGS. 4B-4W are flowcharts of illustrative details of the method of FIG.4A.

FIG. 5A is a flowchart of an illustrative method of operating a nuclearfission traveling wave reactor having a fast neutron spectrum.

FIGS. 5B-5X are flowcharts of illustrative details of the method of FIG.5A.

FIG. 6A is a block diagram of an illustrative system for controllingreactivity in a nuclear fission reactor having a fast neutron spectrum.

FIGS. 6B-6P are block diagrams of illustrative details of the system ofFIG. 6A.

FIG. 7A is a flowchart of an illustrative method of determining anapplication of a controllably movable rod.

FIGS. 7B-7G are flowcharts of illustrative details of the method of FIG.7A.

FIG. 8A is a block diagram of an illustrative system for determining anapplication of a controllably movable rod.

FIGS. 8B-8I are block diagrams of illustrative details of the system ofFIG. 8A.

FIG. 9A is a flowchart of an illustrative method of operating a nuclearfission traveling wave reactor.

FIGS. 9B-9G are flowcharts of illustrative details of the method of FIG.9A.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. The illustrative embodiments described in thedetailed description, drawings, and claims are not meant to be limiting.Other embodiments may be utilized, and other changes may be made,without departing from the spirit or scope of the subject matterpresented here.

The present application uses formal outline headings for clarity ofpresentation. However, it is to be understood that the outline headingsare for presentation purposes, and that different types of subjectmatter may be discussed throughout the application (e.g.,device(s)/structure(s) may be described under process(es)/operationsheading(s) and/or process(es)/operations may be discussed understructures)/process(es) headings; and/or descriptions of single topicsmay span two or more topic headings). Hence, the use of the formaloutline headings is not intended to be in any way limiting.

Illustrative Reactivity Control Assembly

Referring now to FIG. 1A and given by way of overview, an illustrativereactivity control assembly 10 for a nuclear fission reactor (not shown)is shown. A reactivity control rod 12 includes neutron absorbingmaterial 14 configured to absorb neutrons (not shown). At least aportion of the neutron absorbing material 14 includes fertile nuclearfission fuel material 16. At least one sensor 18 is physicallyassociated with the reactivity control rod 12. The sensor 18 isconfigured to sense status of at least one reactivity parameterassociated with the reactivity control rod 12. Illustrative details willbe set forth below by way of non-limiting examples.

It will be appreciated that the reactivity control rod 12 may be anytype of suitable reactivity control rod. In some embodiments thereactivity control rod 12 may be a stand-alone reactivity control rod.That is, in such an arrangement the reactivity control rod 12 is notgrouped into an assembly with other rods, such as nuclear fission fuelrods and/or other reactivity control rods. In some other embodiments,the reactivity control rod 12 may be part of an assembly that includesnuclear fission fuel rods and/or other reactivity control rods.

It will also be appreciated that the reactivity control rod 12 may haveany physical shape as desired for a particular application. Given by wayof non-limiting examples, in various embodiments the reactivity controlrod 12 may have a cross-sectional shape that is square, rectangular,circular, ovoid, or any shape as desired. In various embodiments thereactivity control rod 12 may be embodied as a blade, and may have anycross-sectional shape as desired, such as a rectangle, an “X”, a “+”, orany other shape. The reactivity control rod 12 may have any shape thatis suited for the nuclear fission reactor in which the reactivitycontrol rod 12 is to be used. No limitation regarding shape of thereactivity control rod 12 is implied, and none should be inferred.

In some embodiments the neutron absorbing material 14 may be configuredto absorb fast spectrum neutrons. For example, the neutron absorbingmaterial 14 may have an absorption cross-section that permits absorptionof fast spectrum neutrons—that is, neutrons having an energy level onthe order of at least around 0.11 MeV. Given by way of non-limitingexample, the neutron absorbing material 14 may have an absorptioncross-section on the order of around 10 barns or less. In someembodiments the fertile nuclear fission fuel material 16 may serve asthe component of the neutron absorbing material 14 that absorbs the fastneutrons. In some other embodiments, other component(s) of the neutronabsorbing material 14 may also serve as additional component(s) of theneutron absorbing material 14 (in addition to the fertile nuclearfission fuel material 16) that absorbs the fast neutrons. Illustrativedetails regarding fertile nuclear fission fuel material 16 and othercomponents of the neutron absorbing material 14 will be set forth below.

In some applications, it may be desirable to maintain the neutronspectrum of a nuclear fission reactor within the fast neutron spectrum.Given by way of non-limiting examples, the reactivity control assembly10 may be used to help control reactivity in a fast nuclear fissionreactor, such as without limitation a traveling wave reactor or a fastbreeder reactor, like a liquid metal fast breeder reactor or agas-cooled fast breeder reactor, or the like. To that end, in some otherembodiments the neutron absorbing material 14 may be configured toreduce moderation of neutrons. For example, the neutron absorbingmaterial 14 may have a suitably large atomic mass that can help reducethe amount of slowing down of fast spectrum neutrons. As such, areduction may be made in softening of the neutron spectrum from the fastneutron spectrum toward neutron spectrums having neutron energy levelsless than around 0.1 MeV, such as an epi-thermal neutron spectrum or athermal neutron spectrum. It will be appreciated that, given by way ofnon-limiting examples, elements of the actinide series, such as withoutlimitation uranium and thorium, present a sufficiently large atomic massto help reduce moderation of neutrons.

In some embodiments the fast spectrum neutrons may be part of a nuclearfission traveling wave. A nuclear fission traveling wave may also bereferred to as a nuclear fission deflagration wave. Non-limitingexamples of initiation and propagation of a nuclear fission travelingwave is described in U.S. patent application Ser. No. 11/605,943,entitled AUTOMATED NUCLEAR POWER REACTOR FOR LONG-TERM OPERATION, namingRODERICK A. HYDE, MURIEL Y. ISHIKAWA, NATHAN P. MYHRVOLD, and LOWELL L.WOOD, JR. as inventors, filed 28 Nov. 2006; U.S. patent application Ser.No. 11/605,848, entitled METHOD AND SYSTEM FOR PROVIDING FUEL IN ANUCLEAR REACTOR, naming RODERICK A. HYDE, MURIEL Y. ISHIKAWA, NATHAN P.MYHRVOLD, and LOWELL L. WOOD, JR. as inventors, filed 28 Nov. 2006; andU.S. patent application Ser. No. 11/605,933, entitled CONTROLLABLE LONGTERM OPERATION OF A NUCLEAR REACTOR, naming RODERICK A. HYDE, MURIEL Y.ISHIKAWA, NATHAN P. MYHRVOLD, and LOWELL L. WOOD, JR. as inventors,filed 28 Nov. 2006, the entire contents of which are hereby incorporatedby reference.

The fertile nuclear fission fuel material 16, that is included in theneutron absorbing material 14, can include any type of fertile nuclearfission fuel material as desired for a particular application. Forexample, in some embodiments the fertile nuclear fission fuel material16 may include uranium, such as ²³⁸U. It will be appreciated that theabsorption cross-spectrum for fast neutrons of ²³⁸U is on the order ofaround 0.2 barns. In some other embodiments the fertile nuclear fissionfuel material 16 may include thorium, such as ²³²Th. It will beappreciated that the absorption cross-spectrum for fast neutrons of²³²Th is on the order of around 0.2 barns. The fertile nuclear fissionfuel material 16 may be provided in any suitable form as desired, suchas without limitation powdered form, discrete particle form like beadsor pellets, or any other form as desired.

In some applications it may be desirable to soften the neutron spectrumfrom the fast neutron spectrum toward neutron spectrums having neutronenergy levels less than around 0.1 MeV, such as an epi-thermal neutronspectrum or a thermal neutron spectrum. For example, in suchapplications the reactivity control assembly 10 may be used to helpcontrol reactivity in a thermal nuclear fission reactor, such as withoutlimitation a pressurized water reactor. As another example, in someother applications the reactivity control assembly 10 may be used tohelp control reactivity in a fast nuclear fission reactor in which it isdesired to soften the neutron spectrum to reduce irradiation damage. Tothat end and referring now to FIGS. 1B-1G, in some embodiments thereactivity control rod 12 may also include neutron moderating material20 in addition to the fertile nuclear fission fuel material 16. Theneutron moderating material 20 may include any suitable neutronmoderating material as desired for a particular application. Given byway of non-limiting example, the neutron moderating material 20 mayinclude any one or more of hydrogen, deuterium, helium, lithium, boron,carbon, graphite, sodium, lead, and the like.

When the neutron moderating material 20 is provided, the neutronmoderating material 20 may be distributed within the reactivity controlrod 12 in any manner as desired for a particular application. Forexample and as shown in FIGS. 1B-1F by way of illustration and not oflimitation, in some embodiments the neutron moderating material 20 maybe substantially heterogeneously distributed within the reactivitycontrol rod 12. Given by way of non-limiting examples, the neutronmoderating material 20 may be heterogeneously distributed in disks 21(FIGS. 1B and 1C). The disks 21 may be oriented substantially coaxiallywith an axial orientation of the reactivity control rod 12 (as shown inFIG. 1B) or substantially transverse to the axial orientation of thereactivity control rod 12 (as shown in FIG. 1C). Given by way of furthernon-limiting examples, the neutron moderating material 20 may beheterogeneously distributed toward ends of the reactivity control rod 12(as shown in FIG. 1D) or toward a middle of the reactivity control rod12 (as shown in FIG. 1E). Given by way of a further non-limitingexample, the neutron moderating material 20 may be provided as a rodfollower 23 (as shown in FIG. 1F). It will be appreciated that anyheterogeneous distribution may be used as desired. No particularheterogeneous distribution is intended to be implied by way ofillustration and none should be inferred. In some other embodiments andas shown in FIG. 1G, the neutron moderating material 20 may besubstantially homogeneously distributed within the reactivity controlrod 12.

Referring now to FIGS. 1H-1M, in some embodiments the neutron absorbingmaterial 14 may also include neutron absorbing poison 22 in addition tothe fertile nuclear fission fuel material 16. The neutron absorbingpoison 22 may include any suitable neutron absorbing poison as desired.For example and given by way of non-limiting examples, the neutronabsorbing poison 22 may include any one or more of silver, indium,cadmium, gadolinium, hafnium, lithium, ³He, fission products,protactinium, neptunium, boron, and the like. The neutron absorbingpoison 22 may be provided in any suitable form as desired, such aswithout limitation powdered form, discrete particle form like beads orpellets, or any other form as desired.

When the neutron absorbing poison 22 is provided, the neutron absorbingpoison 22 may be distributed within the reactivity control rod 12 in anymanner as desired for a particular application. For example and as shownin FIGS. 1H-1L by way of illustration and not of limitation, in someembodiments the neutron absorbing poison 22 may be substantiallyheterogeneously distributed within the reactivity control rod 12. Givenby way of non-limiting examples, the neutron absorbing poison 22 may beheterogeneously distributed in disks 25 (FIGS. 1H and 1I. The disks 25may be oriented substantially coaxially with an axial orientation of thereactivity control rod 12 (as shown in FIG. 1H) or substantiallytransverse to the axial orientation of the reactivity control rod 12 (asshown in FIG. 1I). Given by way of further non-limiting examples, theneutron absorbing poison 22 may be heterogeneously distributed towardends of the reactivity control rod 12 (as shown in FIG. 1J) or toward amiddle of the reactivity control rod 12 (as shown in FIG. 1K). Given byway of a further non-limiting example, the neutron absorbing poison 22may be provided as a rod follower 27 (as shown in FIG. 1L). It will beappreciated that any heterogeneous distribution may be used as desired.No particular heterogeneous distribution is intended to be implied byway of illustration and none should be inferred. In some otherembodiments and as shown in FIG. 1M, the neutron absorbing poison 22 maybe substantially homogeneously distributed within the reactivity controlrod 12.

In some embodiments and referring now to FIGS. 1H-1P, an effect onreactivity achievable by the fertile nuclear fission fuel material 16may equalized toward an effect on reactivity achievable by portions ofthe neutron absorbing poison 22. For example, such equalization may bedesirable to mitigate localized flux peaking. It will be appreciatedthat such equalization may be effected regardless of whether the fertilenuclear fission fuel material 16 is distributed heterogeneously orhomogeneously and regardless of whether the neutron absorbing poison 22is distributed heterogeneously (FIGS. 1H-1L and FIGS. 1O-1P) orhomogeneously (FIG. 1M).

In some other embodiments and still referring to FIGS. 1H-1P, reactivityeffect of the fertile nuclear fission fuel material 16 and reactivityeffect of the neutron absorbing poison 22 may be locally tailored asdesired for a particular application. For example, in some embodimentsand as shown generally in FIG. 1N the reactivity control rod 12 has aregion 24 and a region 26. It will be appreciated that the regions 24and 26 may be located anywhere within the reactivity control rod 12 asdesired. No limitation is implied, and is not to be inferred, by virtueof appearance in the drawings which are provided for illustrationpurposes only. A concentration 28 of the neutron absorbing poison 22 isdisposed in the region 24 and a concentration 30 of the neutronabsorbing poison 22 is disposed in the region 26. A concentration 32 ofthe fertile nuclear fission fuel material 16 is disposed in the region24 and a concentration 34 of the fertile nuclear fission fuel material16 is disposed in the region 26. It will be appreciated thatconcentration may be determined per volume basis, per area basis, or perlength basis, as desired.

It will be appreciated that reactivity effects of the concentrations 28and 30 of the neutron absorbing poison 22 and reactivity effects of theconcentrations 32 and 34 of the fertile nuclear fission fuel material 16may be tailored as desired for a particular application. For example, insome embodiments and as shown in FIGS. 1H-1P a reactivity effect of theconcentration 30 of the neutron absorbing poison 22 may be substantiallyequalized with a reactivity effect of the concentration 32 of thefertile nuclear fission fuel material 16. In some other embodiments andas also shown in FIGS. 1H-1P a reactivity effect of the concentration 28of the neutron absorbing poison 22 may be substantially equalized with areactivity effect of the concentration 34 of the fertile nuclear fissionfuel material 16.

In some other embodiments and as shown in FIGS. 1H-1P a reactivityeffect of the concentration 30 of the neutron absorbing poison 22 may bedifferent from a reactivity effect of the concentration 32 of thefertile nuclear fission fuel material 16. In other embodiments areactivity effect of the concentration 28 of the neutron absorbingpoison 22 may be different from a reactivity effect of the concentration34 of the fertile nuclear fission fuel material 16.

Other reactivity effects may be effected as desired. For example and asshown in FIGS. 1H-1P, in some embodiments a sum of reactivity effects ofthe concentration 28 of the neutron absorbing poison 22 and theconcentration 32 of the fertile nuclear fission fuel material 16 may besubstantially equalized toward a sum of reactivity effects of theconcentration 30 of the neutron absorbing poison 22 and theconcentration 34 of the fertile nuclear fission fuel material 16. Insome other embodiments, reactivity effect is substantially constantbetween the region 24 and the region 26.

If desired, concentration of the fertile nuclear fission fuel material16 and/or the neutron absorbing poison 22 may vary. For example and asshown in FIGS. 1O and 1P, in some embodiments concentration the fertilenuclear fission fuel material 16 and/or the neutron absorbing poison 22may change along a continuous gradient. Given by way of non-limitingexample, as shown in FIG. 1O the fertile nuclear fission fuel material16 and the neutron absorbing poison 22 may be provided in wedges 36 and38, respectively, that abut each other along their hypotenuse 40. Givenby way of another non-limiting example, as shown in FIG. 1P the fertilenuclear fission fuel material 16 and the neutron absorbing poison 22 maybe provided in mated frustoconical sections 42 and 44, respectively. Itwill be appreciated that the fertile nuclear fission fuel material 16and the neutron absorbing poison 22 may be provided in other suitablearrangements in which their concentrations change along a continuousgradient, and arrangements are not to be limited to those shown in FIGS.1G and 1H by way of illustration and not of limitation.

In some other embodiments, concentration of the fertile nuclear fissionfuel material 16 and/or the neutron absorbing poison 22 may change alonga non-continuous gradient. For example, concentration of the fertilenuclear fission fuel material 16 and/or the neutron absorbing poison 22may change along a non-continuous gradient as a result of heterogeneousdistribution as shown in FIGS. 1H-1L. In such cases, concentration ofthe neutron absorbing poison 22 can vary along a non-contiguous gradientbecause the neutron absorbing poison 22 is provided in discretelocations (as opposed to homogeneous distribution). Also in such cases,concentration of the fertile nuclear fission fuel material 16 can varyalong a non-contiguous gradient because the fertile nuclear fission fuelmaterial 16 is provided in discrete locations that are separated fromeach other by the discrete locations of the neutron absorbing poison 22.

In some embodiments the fertile nuclear fission fuel material 16 and theneutron absorbing poison 22 may be spatially fixed relative to eachother. That is, in such arrangements the fertile nuclear fission fuelmaterial 16 and the neutron absorbing poison 22 do not physically movein relation to each other. However, in some other embodiments thefertile nuclear fission fuel material 16 and the neutron absorbingpoison 22 may be spatially movable relative to each other. Given by wayof non-limiting example and referring briefly to FIGS. 1H-1L and 1O-1P,any one or more of the discrete locations of the neutron absorbingpoison 22, such as without limitation the disks 25, may be slidablyreceived in the reactivity control rod 12 and may be moved in and out ofthe reactivity control rod 12 as desired by a suitable mechanism, suchas a control rod drive mechanism (not shown) or the like.

The sensor 18 may be physically associated with the reactivity controlrod 12 in any suitable physical association as desired. For example,referring now to FIGS. 1A-1P and also to FIG. 1Q, in some embodimentsphysical association may include the sensor 18 being located within aninterior 46 of the reactivity control rod 12. For example, the sensor 18may be located via any suitable attachment method on an interior surface48 of a cladding wall 50 of the reactivity control rod 12. As a furtherexample and referring now to FIGS. 1A-1P and also to FIG. 1R, in someother embodiments physical association may include the sensor 18 beinglocated proximate an exterior 52 of the reactivity control rod 12. Forexample, the sensor 18 may be located via any suitable method on anexterior surface 54 of the cladding wall 50.

Any one or more of various reactivity parameters associated with thereactivity control rod 12 may be sensed with the sensor 18. Given by wayof non-limiting examples, the sensed reactivity parameter may includeany one or more of parameters such as neutron fluence, neutron flux,neutron fissions, fission products, radioactive decay events,temperature, pressure, power, isotopic concentration, burnup, and/orneutron spectrum.

The sensor 18 may include any suitable sensor that is configured tosense the reactivity parameter that is desired to be sensed. Given byway of non-limiting example, in some embodiments the sensor 18 mayinclude at least one fission detector, such as without limitation amicro-pocket fission detector. In some other embodiments the sensor 18may include a neutron flux monitor, such as without limitation a fissionchamber and/or an ion chamber. In some embodiments the sensor 18 mayinclude a neutron fluence sensor, such as without limitation anintegrating diamond sensor. In some embodiments the sensor 18 mayinclude a fission product detector, such as without limitation a gasdetector, a β detector, and/or a γ detector. In some embodiments, whenprovided, the fission product detector may configured to measure a ratioof isotope types in fission product gas. In some embodiments the sensor18 may include a temperature sensor. In some other embodiments thesensor 18 may include a pressure sensor. In some embodiments the sensor18 may include a power sensor, such as without limitation a power rangenuclear instrument. In some embodiments, if desired the sensor 18 may bereplaceable.

In some applications it may be desirable to mitigate effects of internalpressure within the reactivity control rod 12 exerted by fissionproducts, such as fission product gases. In such cases and referring nowto FIG. 1S, in some embodiments the reactivity control rod 12 may defineat least one chamber 56 configured to accumulate fission products. Forexample, when provided the chamber 56 may include a plenum 58. In someembodiments the plenum 58 may be located at least one mean free pathλ_(T) for fission-inducing neutrons from the fertile nuclear fissionfuel material 16. In some embodiments a backflow prevention device 60,such as a check valve like a ball check vale or the like, may beprovided to help prevent re-entry into the reactivity control rod 12 offission product gases that have outgassed from the reactivity controlrod 12.

Referring now to FIG. 1T, in some embodiments a calibration device 62configured to calibrate the sensor 18 may be provided. It will beappreciated that, when provided, the calibration device 62 suitably is asource having known characteristics or attributes of the reactivityparameter, discussed above, that is sensed by the sensor 18.

Referring now to FIG. 1U, in some embodiments at least onecommunications device 64 may be operatively coupled to the sensor 18 asgenerally indicated at 66. The communications device 18 suitably is anyacceptable device that can operatively couple the sensor 18 in signalcommunication with a suitable communications receiving device (notshown) as generally indicated at 68. Given by way of non-limitingexamples, the communications device 64 may include an electrical cable,a fiber optic cable, a telemetry transmitter, a radiofrequencytransmitter, an optical transmitter, or the like.

Illustrative Reactivity Control System

Referring now to FIG. 2A, an illustrative reactivity control system 210is provided for a nuclear fission reactor (not shown) having a fastneutron spectrum. Given by way of overview, the reactivity controlsystem 210 includes a reactivity control rod 212. The reactivity controlrod 212 includes neutron absorbing material 214 configured to absorbfast spectrum neutrons. At least a portion of the neutron absorbingmaterial 214 includes fertile nuclear fission fuel material 216. Anactuator 217 is responsive to at least one reactivity parameter and isoperationally coupled, as indicated generally at 219, to the reactivitycontrol rod 212. Illustrative details will be set forth below by way ofnon-limiting examples.

The actuator 217 may be responsive to any one or more of variousreactivity parameters as desired for a particular application. In someembodiments, the reactivity parameter may include any one or morereactivity parameter of the nuclear fission reactor. In some otherembodiments the reactivity parameter may include any one or morereactivity parameter of the reactivity control rod 212. Given by way ofnon-limiting examples, the reactivity parameter may include any one ormore of parameters such as neutron fluence, neutron flux, neutronfissions, fission products, radioactive decay events, temperature,pressure, power, isotopic concentration, burnup, and neutron spectrum.

As mentioned above, the nuclear fission reactor (not shown) has a fastneutron spectrum. In some embodiments the nuclear fission reactor mayinclude a traveling wave reactor, in which case the fast spectrumneutrons may be part of a nuclear fission traveling wave. In some otherembodiments the nuclear fission reactor may include a fast breederreactor, like a liquid metal fast breeder reactor or a gas-cooled fastbreeder reactor, or the like.

In some embodiments the neutron absorbing material 214 may be configuredto reduce moderation of neutrons. For example, the neutron absorbingmaterial 14 may have a suitably large atomic mass that can help reducethe amount of slowing down of fast spectrum neutrons. As such, areduction may be made in softening of the neutron spectrum from the fastneutron spectrum toward neutron spectrums having neutron energy levelsless than around 0.1 MeV, such as an epi-thermal neutron spectrum or athermal neutron spectrum. It will be appreciated that, given by way ofnon-limiting examples, elements of the actinide series, such as withoutlimitation uranium and thorium, present a sufficiently large atomic massto help reduce moderation of neutrons.

The fertile nuclear fission fuel material 216, that is included in theneutron absorbing material 214, can include any type of fertile nuclearfission fuel material as desired for a particular application. Forexample, in some embodiments the fertile nuclear fission fuel material216 may include uranium, such as ²³⁸U. In some other embodiments thefertile nuclear fission fuel material 16 may include thorium, such as²³²Th. The fertile nuclear fission fuel material 16 may be provided inany suitable form as desired, such as without limitation powdered form,discrete particle form like beads or pellets, or any other form asdesired.

In some applications it may be desirable to soften the neutron spectrumwithin the fast neutron spectrum toward a softer neutron spectrum thatis still within the fast neutron spectrum—that is, at least around 0.1MeV. For example, in some applications it may be desired to soften theneutron spectrum to reduce irradiation damage. To that end and referringnow to FIGS. 2B-2G, in some embodiments the reactivity control rod 212may also include neutron moderating material 220 in addition to thefertile nuclear fission fuel material 216. The neutron moderatingmaterial 220 may include any suitable neutron moderating material asdesired for a particular application. Given by way of non-limitingexample, the neutron moderating material 220 may include any one or moreof hydrogen, deuterium, helium, lithium, boron, carbon, graphite,sodium, lead, and the like.

When the neutron moderating material 220 is provided, the neutronmoderating material 220 may be distributed within the reactivity controlrod 212 in any manner as desired for a particular application. Forexample and as shown in FIGS. 2B-2F by way of illustration and not oflimitation, in some embodiments the neutron moderating material 220 maybe substantially heterogeneously distributed within the reactivitycontrol rod 212. Given by way of non-limiting examples, the neutronmoderating material 220 may be heterogeneously distributed in disks 221(FIGS. 2B and 2C). The disks 221 may be oriented substantially coaxiallywith an axial orientation of the reactivity control rod 212 (as shown inFIG. 2B) or substantially transverse to the axial orientation of thereactivity control rod 212 (as shown in FIG. 2C). Given by way offurther non-limiting examples, the neutron moderating material 220 maybe heterogeneously distributed toward ends of the reactivity control rod212 (as shown in FIG. 2D) or toward a middle of the reactivity controlrod 212 (as shown in FIG. 2E). Given by way of a further non-limitingexample, the neutron moderating material 220 may be provided as a rodfollower 223 (as shown in FIG. 2F). It will be appreciated that anyheterogeneous distribution may be used as desired. No particularheterogeneous distribution is intended to be implied by way ofillustration and none should be inferred. In some other embodiments andas shown in FIG. 2G, the neutron moderating material 220 may besubstantially homogeneously distributed within the reactivity controlrod 212.

Referring now to FIGS. 2H-2M, in some embodiments the neutron absorbingmaterial 214 may also include neutron absorbing poison 222 in additionto the fertile nuclear fission fuel material 216. The neutron absorbingpoison 222 may include any suitable neutron absorbing poison as desired.For example and given by way of non-limiting examples, the neutronabsorbing poison 222 may include any one or more of silver, indium,cadmium, gadolinium, hafnium, lithium, ³He, fission products,protactinium, neptunium, boron, and the like. The neutron absorbingpoison 222 may be provided in any suitable form as desired, such aswithout limitation powdered form, discrete particle form like beads orpellets, or any other form as desired.

When the neutron absorbing poison 222 is provided, the neutron absorbingpoison 222 may be distributed within the reactivity control rod 212 inany manner as desired for a particular application. For example and asshown in FIGS. 2H-2L by way of illustration and not of limitation, insome embodiments the neutron absorbing poison 222 may be substantiallyheterogeneously distributed within the reactivity control rod 212. Givenby way of non-limiting examples, the neutron absorbing poison 222 may beheterogeneously distributed in disks 225 (FIGS. 2H and 2I). The disks225 may be oriented substantially coaxially with an axial orientation ofthe reactivity control rod 212 (as shown in FIG. 2H) or substantiallytransverse to the axial orientation of the reactivity control rod 212(as shown in FIG. 2I). Given by way of further non-limiting examples,the neutron absorbing poison 222 may be heterogeneously distributedtoward ends of the reactivity control rod 212 (as shown in FIG. 2J) ortoward a middle of the reactivity control rod 212 (as shown in FIG. 2K).Given by way of a further non-limiting example, the neutron absorbingpoison 222 may be provided as a rod follower 227 (as shown in FIG. 2L).It will be appreciated that any heterogeneous distribution may be usedas desired. No particular heterogeneous distribution is intended to beimplied by way of illustration and none should be inferred. In someother embodiments and as shown in FIG. 2M, the neutron absorbing poison222 may be substantially homogeneously distributed within the reactivitycontrol rod 212.

In some embodiments and referring now to FIGS. 2H-2P, an effect onreactivity achievable by the fertile nuclear fission fuel material 216may equalized toward an effect on reactivity achievable by portions ofthe neutron absorbing poison 222. For example, such equalization may bedesirable to mitigate localized flux peaking. It will be appreciatedthat such equalization may be effected regardless of whether the fertilenuclear fission fuel material 216 is distributed heterogeneously orhomogeneously and regardless of whether the neutron absorbing poison 222is distributed heterogeneously (FIGS. 2H-2L and FIGS. 2O-2P) orhomogeneously (FIG. 2M).

In some other embodiments and still referring to FIGS. 2H-2P, reactivityeffect of the fertile nuclear fission fuel material 216 and reactivityeffect of the neutron absorbing poison 222 may be locally tailored asdesired for a particular application. For example, in some embodimentsand as shown generally in FIG. 2N the reactivity control rod 212 has aregion 224 and a region 226. It will be appreciated that the regions 224and 226 may be located anywhere within the reactivity control rod 212 asdesired. No limitation is implied, and is not to be inferred, by virtueof appearance in the drawings which are provided for illustrationpurposes only. A concentration 228 of the neutron absorbing poison 222is disposed in the region 224 and a concentration 230 of the neutronabsorbing poison 222 is disposed in the region 226. A concentration 232of the fertile nuclear fission fuel material 216 is disposed in theregion 224 and a concentration 234 of the fertile nuclear fission fuelmaterial 216 is disposed in the region 226. It will be appreciated thatconcentration may be determined per volume basis, per area basis, or perlength basis, as desired.

It will be appreciated that reactivity effects of the concentrations 228and 230 of the neutron absorbing poison 222 and reactivity effects ofthe concentrations 232 and 234 of the fertile nuclear fission fuelmaterial 216 may be tailored as desired for a particular application.For example, in some embodiments and as shown in FIGS. 2H-2P areactivity effect of the concentration 230 of the neutron absorbingpoison 222 may be substantially equalized with a reactivity effect ofthe concentration 232 of the fertile nuclear fission fuel material 216.In some other embodiments and as also shown in FIGS. 2H-2P a reactivityeffect of the concentration 228 of the neutron absorbing poison 222 maybe substantially equalized with a reactivity effect of the concentration234 of the fertile nuclear fission fuel material 216.

In some other embodiments and as shown in FIGS. 2H-2P a reactivityeffect of the concentration 230 of the neutron absorbing poison 222 maybe different from a reactivity effect of the concentration 232 of thefertile nuclear fission fuel material 216. In other embodiments areactivity effect of the concentration 228 of the neutron absorbingpoison 222 may be different from a reactivity effect of theconcentration 234 of the fertile nuclear fission fuel material 216.

Other reactivity effects may be affected as desired. For example and asshown in FIGS. 2H-2P, in some embodiments a sum of reactivity effects ofthe concentration 228 of the neutron absorbing poison 222 and theconcentration 232 of the fertile nuclear fission fuel material 216 maybe substantially equalized toward a sum of reactivity effects of theconcentration 230 of the neutron absorbing poison 222 and theconcentration 234 of the fertile nuclear fission fuel material 216. Insome other embodiments, reactivity effect is substantially constantbetween the region 224 and the region 226.

If desired, concentration of the fertile nuclear fission fuel material216 and/or the neutron absorbing poison 222 may vary. For example and asshown in FIGS. 2O and 2P, in some embodiments concentration the fertilenuclear fission fuel material 216 and/or the neutron absorbing poison222 may change along a continuous gradient. Given by way of non-limitingexample, as shown in FIG. 2O the fertile nuclear fission fuel material216 and the neutron absorbing poison 222 may be provided in wedges 236and 238, respectively, that abut each other along their hypotenuse 240.Given by way of another non-limiting example, as shown in FIG. 2P thefertile nuclear fission fuel material 216 and the neutron absorbingpoison 222 may be provided in mated frustoconical sections 242 and 244,respectively. It will be appreciated that the fertile nuclear fissionfuel material 216 and the neutron absorbing poison 222 may be providedin other suitable arrangements in which their concentrations changealong a continuous gradient, and arrangements are not to be limited tothose shown in FIGS. 2G and 2H by way of illustration and not oflimitation.

In some other embodiments, concentration of the fertile nuclear fissionfuel material 216 and/or the neutron absorbing poison 222 may changealong a non-continuous gradient. For example, concentration of thefertile nuclear fission fuel material 216 and/or the neutron absorbingpoison 222 may change along a non-continuous gradient as a result ofheterogeneous distribution as shown in FIGS. 2H-2L. In such cases,concentration of the neutron absorbing poison 222 can vary along anon-contiguous gradient because the neutron absorbing poison 222 isprovided in discrete locations (as opposed to homogeneous distribution).Also in such cases, concentration of the fertile nuclear fission fuelmaterial 216 can vary along a non-contiguous gradient because thefertile nuclear fission fuel material 216 is provided in discretelocations that are separated from each other by the discrete locationsof the neutron absorbing poison 222.

In some embodiments the fertile nuclear fission fuel material 216 andthe neutron absorbing poison 222 may be spatially fixed relative to eachother. That is, in such arrangements the fertile nuclear fission fuelmaterial 216 and the neutron absorbing poison 222 do not physically movein relation to each other. However, in some other embodiments thefertile nuclear fission fuel material 216 and the neutron absorbingpoison 222 may be spatially movable relative to each other. Given by wayof non-limiting example and referring briefly to FIGS. 2H-2L and 2O-2P,any one or more of the discrete locations of the neutron absorbingpoison 222, such as without limitation the disks 225, may be slidablyreceived in the reactivity control rod 212 and may be moved in and outof the reactivity control rod 212 as desired by a suitable mechanism,such as a control rod drive mechanism or the like.

Referring now to FIG. 2Q, in some embodiments the reactivity control rod212 may define at least one chamber 256 configured to accumulate fissionproducts. For example, when provided the chamber 256 may include aplenum 258. In some embodiments the plenum 258 may be located at leastone mean free path λ_(T) for fission-inducing neutrons from the fertilenuclear fission fuel material 216. In some embodiments a backflowprevention device 260, such as a check valve like a ball check vale orthe like, may be provided to help prevent re-entry into the reactivitycontrol rod 212 of fission product gases that have outgassed from thereactivity control rod 212.

As mentioned above, the actuator 217 is responsive to at least onereactivity parameter. In some embodiments, the reactivity control system210 may include an apparatus configured to determine the reactivityparameter. Given by way of non-limiting examples and referring now toFIGS. 2R-2AL, the apparatus may include at least one sensor 218.

As shown in FIGS. 2R-2AL, in some embodiments the sensor 218 may bephysically associated with the reactivity control rod 210. Given by wayof non-limiting examples, in FIGS. 2R-2AI, the sensor 218 may bephysically associated with embodiments of the reactivity control rod 210that have been shown and explained with reference to FIGS. 2A-2Q. Insuch cases, details have already been set forth regarding embodiments ofthe reactivity control rod 210 with reference to FIGS. 2A-2Q and neednot be repeated for an understanding.

In such embodiments the sensor 218 may be physically associated with thereactivity control rod 212 in any suitable physical association asdesired. For example and referring to FIG. 2AI, in some embodimentsphysical association may include the sensor 218 being located within aninterior 246 of the reactivity control rod 212. For example, the sensor218 may be located via any suitable attachment method on an interiorsurface 248 of a cladding wall 250 of the reactivity control rod 212. Asa further example and referring now to FIG. 2AJ, in some otherembodiments physical association may include the sensor 218 beinglocated proximate an exterior 252 of the reactivity control rod 212. Forexample, the sensor 218 may be located via any suitable method on anexterior surface 254 of the cladding wall 250.

It will be appreciated that the sensor 218 need not be physicallyassociated with the reactivity control rod 212. To that end, in someembodiments, the sensor 218 is not physically associated with thereactivity control rod 212. For example, in some embodiments the sensor218 may be located at a position that is separate from the reactivitycontrol rod 212 but that permits the sensor 218 to sense the reactivityparameter desired to be sensed. Given by way of non-limiting example,the sensor 218 may be located at a position that is separate but no morethan one mean free path λ_(T) for fission-inducing neutrons from thereactivity control rod 212.

Any one or more of various reactivity parameters associated with thereactivity control rod 212 may be sensed with the sensor 218. Given byway of non-limiting examples, the sensed reactivity parameter mayinclude any one or more of parameters such as neutron fluence, neutronflux, neutron fissions, fission products, radioactive decay events,temperature, pressure, power, isotopic concentration, burnup, and/orneutron spectrum.

The sensor 218 may include any suitable sensor that is configured tosense the reactivity parameter that is desired to be sensed. Given byway of non-limiting example, in some embodiments the sensor 218 mayinclude at least one fission detector, such as without limitation amicro-pocket fission detector. In some other embodiments the sensor 218may include a neutron flux monitor, such as without limitation a fissionchamber and/or an ion chamber. In some embodiments the sensor 218 mayinclude a neutron fluence sensor, such as without limitation anintegrating diamond sensor. In some embodiments the sensor 218 mayinclude a fission product detector, such as without limitation a gasdetector, a β detector, and/or a γ detector. In some embodiments, whenprovided, the fission product detector may be configured to measure aratio of isotope types in fission product gas. In some embodiments thesensor 18 may include a temperature sensor. In some other embodimentsthe sensor 218 may include a pressure sensor. In some embodiments thesensor 218 may include a power sensor, such as without limitation apower range nuclear instrument. In some embodiments, if desired thesensor 218 may be replaceable.

In some other embodiments, the reactivity parameter may be determinedwithout being sensed by a sensor. Given by way of non-limiting example,in some embodiments the apparatus may include electrical circuitry (notshown) configured to determine at least one reactivity parameter (whichhave been discussed above). The reactivity parameter may be determinedin any suitable manner. Given by way of non-limiting example, thereactivity parameter may be retrieved from a look-up table usingoperating parameters, such as temperature, pressure, power level, timein core life (as measured in effective full power hours), and the like,as entering arguments. Given by way of another non-limiting example, thereactivity parameter may be modeled, such as by running suitableneutronics modeling software on a suitable computer. Given by way ofillustration, suitable neutronics modeling software includes MCNP,CINDER, REBUS, and the like. In a further non-limiting example, thereactivity parameter may be determined by a reactor operator or anyother person skilled in the art based on prior knowledge or experience.

In a general sense, those skilled in the art will recognize that variousaspects described herein (including the electrical circuitry configuredto determine at least one reactivity parameter) can be implemented,individually and/or collectively, by a wide range of hardware, software,firmware, or any combination thereof that can be viewed as beingcomposed of various types of “electrical circuitry.” Consequently, asused herein “electrical circuitry” includes, but is not limited to,electrical circuitry having at least one discrete electrical circuit,electrical circuitry having at least one integrated circuit, electricalcircuitry having at least one application specific integrated circuit,electrical circuitry forming a general purpose computing deviceconfigured by a computer program (e.g., a general purpose computerconfigured by a computer program which at least partially carries outprocesses and/or devices described herein, or a microprocessorconfigured by a computer program which at least partially carries outprocesses and/or devices described herein), electrical circuitry forminga memory device (e.g., forms of random access memory), and/or electricalcircuitry forming a communications device (e.g., a modem, communicationsswitch, or optical-electrical equipment). Those having skill in the artwill recognize that the subject matter described herein may beimplemented in an analog or digital fashion or some combination thereof.

Referring to FIG. 2AK, in some embodiments a calibration device 262configured to calibrate the sensor 218 may be provided. It will beappreciated that, when provided, the calibration device 262 suitably isa source having known characteristics or attributes of the reactivityparameter, discussed above, that is sensed by the sensor 218.

Referring to FIG. 2AL, in some embodiments at least one communicationsdevice 264 may be operatively coupled to the sensor 218 as generallyindicated at 266. The communications device 218 suitably is anyacceptable device that can operatively couple the sensor 218 in signalcommunication with a suitable communications receiving device (notshown) as generally indicated at 268. Given by way of non-limitingexamples, the communications device 264 may include an electrical cable,a fiber optic cable, a telemetry transmitter, a radiofrequencytransmitter, an optical transmitter, or the like.

Referring now to FIGS. 2A-2AL, the reactivity control rod 212 isoperationally coupled, as indicated generally at 219, to the actuator217 in any suitable manner as desired. For example, in some embodimentsthe reactivity control rod 212 may be electromagnetically coupled to theactuator 217. In some other embodiments the reactivity control rod 212may be mechanically linked to the actuator 217.

Referring to FIG. 2AM, in some embodiments the reactivity control system210 may include an actuator controller 270 that is configured togenerate a rod control signal 272. In such embodiments, the actuator 217is configured to move the reactivity control rod 217 that isoperationally coupled thereto (as generally indicated at 219) responsiveto the rod control signal 272.

The actuator controller 270 generates the rod control signal 272 andcommunicates the rod control signal 272 in signal communication to theactuator 217. Referring to FIG. 2AN, in some embodiments acommunications device 274 is configured to communicate the rod controlsignal 272 from the actuator controller 270 to the actuator 217. Thecommunications device 274 suitably is any acceptable device that canoperatively couple the actuator controller 270 in signal communicationwith the actuator 217. Given by way of non-limiting examples, thecommunications device 274 may include an electrical cable, a fiber opticcable, a telemetry transmitter, a radiofrequency transmitter, an opticaltransmitter, or the like.

The actuator controller 270 may generate the rod control signal 272 inany suitable manner as desired. For example and referring to FIG. 2AO,in some embodiments the actuator controller 270 may include an operatorinterface 276. Given by way of non-limiting example, in some embodimentsthe operator interface 276 may include a shim switch.

Referring to FIG. 2AP, in some other embodiments the actuator controller270 may include electrical circuitry 278 that is configured toautomatically generate the rod control signal 272 based upon at leastone reactivity parameter (which have been discussed above).

Referring now to FIGS. 2A-2AP, the actuator 217 may be any suitableactuator as desired for a particular application. Given by way ofnon-limiting example, in some embodiments the actuator 217 may include areactivity control rod drive mechanism. In some embodiments the actuator217 may be configured to drive the reactivity control rod 212bidirectionally. That is, when the reactivity control rod 212 isprovided for use in a nuclear fission reactor, the reactivity controlrod 212 may be driven into and/or out of a core of the nuclear fissionreactor as desired. In some other embodiments, the actuator 217 may befurther configured to stop driving the reactivity control rod 217 atleast one intermediate position between a first stop position and asecond stop position.

Illustrative Nuclear Fission Traveling Wave Reactor

Referring now to FIG. 3, in some embodiments an illustrative nuclearfission traveling wave reactor 300 having a fast neutron spectrum mayinclude any illustrative embodiment of the reactivity control system 210(FIGS. 2A-2AP).

Given by way of non-limiting example, the nuclear fission traveling wavereactor 300 includes an illustrative nuclear fission reactor core 331.The nuclear fission reactor core 331 includes suitable nuclear fissionfuel material 333 that is configured to propagate therein a nuclearfission traveling wave having a fast neutron spectrum.

As described above, the reactivity control system 210 includesreactivity control rods 212. Each reactivity control rod 212 includesneutron absorbing material configured to absorb fast spectrum neutronsof the nuclear fission traveling wave. At least a portion of the neutronabsorbing material includes fertile nuclear fission fuel material. Thereactivity control system 210 also includes actuators 217. Each of theactuators 217 is responsive to at least one reactivity parameter and isoperationally coupled to at least one of the reactivity control rods212, as indicated generally at 219.

In some embodiments, the reactivity parameter may include at least onereactivity parameter of the nuclear fission traveling wave reactor.However, in some other embodiments and as discussed above, thereactivity parameter may include at least one reactivity parameter of atleast one of the reactivity control rods 212. In various embodiments thereactivity parameter may include one or more reactivity parameters suchas neutron fluence, neutron flux, neutron fissions, fission products,radioactive decay events, temperature, pressure, power, isotopicconcentration, burnup, and/or neutron spectrum.

It will be appreciated that the reactivity control system 210 includedin the nuclear fission traveling wave reactor 300 may be embodied in anymanner desired as discussed above. For example, the reactivity controlsystem and any of its components may be embodied, without limitation, asdiscussed above with reference to any one or more of FIGS. 2A-2AP.Because embodiments of the reactivity control system 210 have beendiscussed in detail above, for sake of brevity details need not berepeated for an understanding.

Illustrative details of embodiments of the nuclear fission travelingwave reactor 300 will be set forth below. It will be appreciated thatthe nuclear fission traveling wave reactor 300 is a non-limiting examplethat is set forth below for purposes of illustration and not oflimitation.

The nuclear fission reactor core 333 is housed within an illustrativereactor core enclosure 335 which acts to maintain vertical coolant flowthrough the core. In some embodiments the reactor core enclosure 335 mayalso function as a radiation shield to protect in-pool components suchas heat exchangers and the like from neutron bombardment. The reactivitycontrol rods 212 longitudinally extend into the nuclear fission reactorcore 331 for controlling the fission process occurring therein, asdiscussed above.

The nuclear fission reactor core 331 is disposed within an illustrativereactor vessel 337. In some embodiments the reactor vessel 337 is filledto a suitable amount (such as about 90% or so) with a pool of coolant339, such as liquid metal like sodium, potassium, lithium, lead,mixtures thereof, and the like, or liquid metal alloys such aslead-bismuth, to such an extent that the nuclear fission reactor core331 is submerged in the pool of coolant. Suitably, in an illustrativeembodiment contemplated herein, the coolant is a liquid sodium (Na)metal or sodium metal mixture, such as sodium-potassium (Na—K). Inaddition, in some embodiments a containment vessel 341 sealinglysurrounds parts of the nuclear fission traveling wave reactor 300.

In some embodiments a primary coolant pipe 343 is coupled to the nuclearfission reactor core 331 for allowing a suitable coolant to flow throughthe nuclear fission reactor core 331 along a coolant flow stream or flowpath 345 in order to cool the nuclear fission reactor core 331. Invarious embodiments the primary coolant pipe 343 may be made frommaterials such as, without limitation, stainless steel or fromnon-ferrous alloys, zirconium-based alloys, or other suitable structuralmaterials or composites.

In some embodiments the heat-bearing coolant generated by the nuclearfission reactor core 331 flows along the coolant flow path 345 to anintermediate heat exchanger 347 that is also submerged in the pool ofcoolant 339. The intermediate heat exchanger 347 may be made from anysuitable material, such as without limitation stainless steel, that issufficiently resistant to heat and corrosive effects of the coolant,such as without limitation liquid sodium, in the pool of coolant 339.The coolant flowing along the coolant flow path 345 flows through theintermediate heat exchanger 347 and continues through the primarycoolant pipe 343. It will be appreciated that the coolant leavingintermediate heat exchanger 347 has been cooled due to heat transferoccurring in the intermediate heat exchanger 347. In some embodiments apump 349, which may be an electro-mechanical pump or an electromagneticpump as desired, is coupled to the primary coolant pipe 343. In suchembodiments the pump 349 is in fluid communication with the coolantcarried by the primary coolant pipe 343. The pump 349 pumps the coolantthrough the primary coolant pipe 343, through the nuclear fissionreactor core 331, along the coolant flow path 345, and into theintermediate heat exchanger 347.

A secondary coolant pipe 351 is provided for removing heat from theintermediate heat exchanger 347. The secondary coolant pipe 351 includesa secondary hot leg pipe segment 353 and a secondary cold leg pipesegment 355. The secondary hot leg pipe segment 353 and the secondarycold leg pipe segment 355 are integrally connected to the intermediateheat exchanger 347. The secondary coolant pipe 351 contains a secondarycoolant, that is a fluid such as any one of the coolant choicespreviously mentioned.

The secondary hot leg pipe segment 353 extends from the intermediateheat exchanger 347 to a steam generator 357. In some embodiments, ifdesired, the steam generator 357 may include a superheater. Afterpassing through the steam generator 357, the secondary coolant flowingthrough the secondary loop pipe 351 and exiting the steam generator 357is at a lower temperature and enthalpy than before entering the steamgenerator 357 due to heat transfer occurring within the steam generator357. After passing through the steam generator 357, the secondarycoolant is pumped, such as by means of a pump 359, which may be anelectro-mechanical pump or an electromagnetic pump or the like, alongthe secondary cold leg pipe segment 355, which extends into theintermediate heat exchanger 347 for providing the previously mentionedheat transfer.

Disposed in the steam generator 357 is a body of water 361 having apredetermined temperature. The secondary coolant flowing through thesecondary hot leg pipe segment 353 will transfer its heat by means ofconduction and convection to the body of water 361, which is at a lowertemperature than the secondary coolant flowing through the secondary hotleg pipe segment 353. As the secondary coolant flowing through thesecondary hot leg pipe segment 353 transfers its heat to the body ofwater 361, a portion of the body of water 361 will vaporize to steam 363according to the predetermined temperature within the steam generator357. The steam 363 will then travel through a steam line 365. One end ofthe steam line 365 is in vapor communication with the steam 363 andanother end of the steam line 365 is in liquid communication with thebody of water 361.

A rotatable turbine 367 is coupled to the steam line 365 such that theturbine 367 rotates as the steam 363 passes therethrough. An electricalgenerator 369 is coupled to the turbine 367 by a rotatable turbine shaft371. The electrical generator 369 generates electricity as the turbine367 rotates.

A condenser 373 is coupled to the steam line 365 and receives the steam363 passing through the turbine 367. The condenser 373 condenses thesteam 363 to liquid water and passes any waste heat via a recirculationfluid path 375 and a condensate pump 377, such as an electro-mechanicalpump, to a heat sink 379, such as a cooling tower, which is associatedwith the condenser 373. The feed water condensed by the condenser 373 ispumped along a feed water line 381 from the condenser 373 to the steamgenerator 357 by a feed water pump 383, which may be anelectro-mechanical pump that is interposed between the condenser 373 andthe steam generator 357.

Embodiments of the nuclear fission reactor core 331 may include anysuitable configuration as desired to accommodate the reactivity controlsystem 210. In this regard, in some embodiments the nuclear fissionreactor core 331 may be generally cylindrically shaped to obtain agenerally circular transverse cross section. In some other embodimentsthe nuclear fission reactor core 331 may be generally hexagonally shapedto obtain a generally hexagonal transverse cross section. In otherembodiments the nuclear fission reactor core 331 may be generallyparallelepiped shaped to obtain a generally rectangular transverse crosssection.

Regardless of the configuration or shape selected for the nuclearfission reactor core 331, the nuclear fission reactor core 331 isoperated as a traveling wave nuclear fission reactor core. For example,a nuclear fission igniter (not shown for clarity), which includes anisotopic enrichment of nuclear fissionable material, such as, withoutlimitation, U-233, U-235 or Pu-239, is suitably located in the nuclearfission reactor core 331. Neutrons are released by the igniter. Theneutrons that are released by the igniter are captured by fissile and/orfertile material within the nuclear fission fuel material 333 toinitiate a nuclear fission chain reaction. The igniter may be removedonce the fission chain reaction becomes self-sustaining, if desired.

The igniter initiates a three-dimensional, traveling wave or “burnwave”. When the igniter generates neutrons to cause “ignition”, the burnwave travels outwardly from the igniter so as to form the traveling orpropagating burn wave. Speed of the traveling burn wave may be constantor non-constant. Thus, the speed at which the burn wave propagates canbe controlled. For example, longitudinal movement of the reactivitycontrol rods 210 in a predetermined or programmed manner can drive downor lower neutronic reactivity of vented nuclear fission fuel modules 30.In this manner, neutronic reactivity of nuclear fuel that is presentlybeing burned behind the burn wave or at the location of the burn wave isdriven down or lowered relative to neutronic reactivity of “unburned”nuclear fuel ahead of the burn wave. Controlling reactivity in thismanner maximizes the propagation rate of the burn wave subject tooperating constraints for the nuclear fission reactor core 331, such asamount of permissible fission product production and/or neutron fluencelimitations of reactor core structural materials.

The basic principles of such a traveling wave nuclear fission reactorare disclosed in more detail in U.S. patent application Ser. No.11/605,943, entitled AUTOMATED NUCLEAR POWER REACTOR FOR LONG-TERMOPERATION, naming RODERICK A. HYDE, MURIEL Y. ISHIKAWA, NATHAN P.MYHRVOLD, and LOWELL L. WOOD, JR. as inventors, filed 28 Nov. 2006; U.S.patent application Ser. No. 11/605,848, entitled METHOD AND SYSTEM FORPROVIDING FUEL IN A NUCLEAR REACTOR, naming RODERICK A. HYDE, MURIEL Y.ISHIKAWA, NATHAN P. MYHRVOLD, and LOWELL L. WOOD, JR. as inventors,filed 28 Nov. 2006; and U.S. patent application Ser. No. 11/605,933,entitled CONTROLLABLE LONG TERM OPERATION OF A NUCLEAR REACTOR, namingRODERICK A. HYDE, MURIEL Y. ISHIKAWA, NATHAN P. MYHRVOLD, and LOWELL L.WOOD, JR. as inventors, filed 28 Nov. 2006, the entire contents of whichare hereby incorporated by reference.

It will be appreciated that the embodiment of the nuclear fissiontraveling wave reactor 300 described above is set forth as anon-limiting example for purposes of illustration only and not oflimitation. In some other embodiments, the nuclear fission travelingwave reactor 300 may be a gas-cooled fast nuclear fission traveling wavereactor that includes a suitable gas coolant, such as helium or thelike. In such an embodiment, a gas-driven turbine-generator may bedriven by the gas coolant.

Illustrative Methods, Systems, and Computer Software Program Products

Following are a series of flowcharts depicting implementations ofprocesses. For ease of understanding, the flowcharts are organized suchthat the initial flowcharts present implementations via an overall “bigpicture” viewpoint and thereafter the following flowcharts presentalternate implementations and/or expansions of the “big picture”flowcharts as either sub-steps or additional steps building on one ormore earlier-presented flowcharts. Those having skill in the art willappreciate that the style of presentation utilized herein (e.g.,beginning with a presentation of a flowchart(s) presenting an overallview and thereafter providing additions to and/or further details insubsequent flowcharts) generally allows for a rapid and easyunderstanding of the various process implementations. In addition, thoseskilled in the art will further appreciate that the style ofpresentation used herein also lends itself well to modular and/orobject-oriented program design paradigms. Also, although the variousoperational flows are presented in the sequence(s) illustrated, itshould be understood that the various operations may be performed inother orders than those which are illustrated, or may be performedconcurrently.

Referring now to FIG. 4A, a method 400 is provided for controllingreactivity in a nuclear fission reactor having a fast neutron spectrum.The method 400 starts at a block 402. At a block 404 a desiredreactivity parameter within a selected portion of the nuclear fissionreactor having a fast neutron spectrum is determined. At a block 406 atleast one reactivity control rod having fast spectrum neutron absorbingmaterial, at least a portion of the fast spectrum neutron absorbingmaterial including fertile nuclear fission fuel material, is adjustedresponsive to the desired reactivity parameter. The method 400 stops ata block 408.

It will be appreciated that the method 400 may be performed with respectto any nuclear fission reactor having a fast neutron spectrum. In someembodiments, the method 400 may be performed with respect to a nuclearfission traveling wave reactor, in which case the fast spectrum neutronsmay be part of a nuclear fission traveling wave. In some otherembodiments, the method 400 may be performed with respect to anysuitable fast breeder reactor, such as a liquid metal fast breederreactor, a gas-cooled fast breeder reactor, or the like. Thus, nolimitation to any particular type of nuclear fission reactor having afast neutron spectrum is intended and should not be inferred.

Illustrative details will be set forth below by way of non-limitingexamples.

In various embodiments the desired reactivity parameter may bedetermined with respect to any portion of a nuclear fission reactor asdesired. For example and referring to FIG. 4B, in some embodimentsdetermining a desired reactivity parameter within a selected portion ofa nuclear fission reactor having a fast neutron spectrum at the block404 may include determining at least one desired reactivity parameter ofthe fertile nuclear fission fuel material at a block 410. In some otherembodiments and referring to FIG. 4C, determining a desired reactivityparameter within a selected portion of a nuclear fission reactor havinga fast neutron spectrum at the block 404 may include determining atleast one desired reactivity parameter of the at least one reactivitycontrol rod at a block 412. In some other embodiments and referring toFIG. 4D, determining a desired reactivity parameter within a selectedportion of a nuclear fission reactor having a fast neutron spectrum atthe block 404 may include determining at least one desired reactivityparameter of the nuclear fission reactor at a block 414.

In some embodiments the reactivity control rod may be adjustedresponsive to a difference between the desired reactivity parameter anda determination of the reactivity parameter. For example and referringto FIGS. 4A and 4E, in some embodiments at a block 416 at least onedetermined reactivity parameter may be determined. Referringadditionally to FIG. 4F, in some embodiments at a block 418 a differencebetween the desired reactivity parameter and the at least one determinedreactivity parameter may be determined. Referring additionally to FIG.4G, in some embodiments adjusting at least one reactivity control rodhaving fast spectrum neutron absorbing material, at least a portion ofthe neutron absorbing material including fertile nuclear fission fuelmaterial, responsive to the desired reactivity parameter at the block406 may include adjusting at least one reactivity control rod havingfast spectrum neutron absorbing material, at least a portion of theneutron absorbing material including fertile nuclear fission fuelmaterial, responsive to the difference between the desired reactivityparameter and the at least one determined reactivity parameter at ablock 420.

The determined reactivity parameter may be determined in any suitablemanner as desired. For example and referring now to FIGS. 4E and 4H, insome embodiments determining at least one determined reactivityparameter at the block 416 may include predicting at least onereactivity parameter at a block 422. Referring to FIGS. 4E and 4I, insome embodiments determining at least one determined reactivityparameter at the block 416 may include modeling at least one reactivityparameter at a block 424. Referring to FIGS. 4E and 4J, in someembodiments determining at least one determined reactivity parameter atthe block 416 may include selecting at least one predeterminedreactivity parameter at a block 426.

Referring to FIGS. 4E and 4K, in some other embodiments determining atleast one determined reactivity parameter at the block 416 may includesensing at least one reactivity parameter at a block 428. It will beappreciated that any desired reactivity parameter may be sensed at theblock 428 in any suitable manner.

For example and referring to FIGS. 4K and 4L, in some embodimentssensing at least one reactivity parameter at the block 428 may includesensing a time history of at least one reactivity parameter at a block430. Sensing a time history may be performed as desired, such as bysensing and recording or storing the sensed reactivity parameter morethan one time. Given by way of non-limiting examples, a time history ofat least one reactivity parameter may include, without limitation, arate of the reactivity parameter, accumulation of the reactivityparameter, total fissions, or the like. Referring to FIGS. 4K and 4M, insome embodiments sensing at least one reactivity parameter at the block428 may include sensing at least one radioactive decay event at a block432. Referring to FIGS. 4K and 4N, in some embodiments sensing at leastone reactivity parameter at the block 428 may include detecting fissionat a block 434. Referring to FIGS. 4K and 4O, in some embodimentssensing at least one reactivity parameter at the block 428 may includemonitoring neutron flux at a block 436. Referring to FIGS. 4K and 4P, insome embodiments sensing at least one reactivity parameter at the block428 may include sensing neutron fluence at a block 438. Referring toFIGS. 4K and 4Q, in some embodiments sensing at least one reactivityparameter at the block 428 may include detecting fission products at ablock 440.

Referring to FIGS. 4K and 4R, in some embodiments sensing at least onereactivity parameter at the block 428 may include sensing temperature ata block 442. Referring to FIGS. 4K and 4S, in some embodiments sensingat least one reactivity parameter at the block 428 may include sensingpressure at a block 444. Referring to FIGS. 4K and 4T, in someembodiments sensing at least one reactivity parameter at the block 428may include sensing power level at a block 446.

Referring now to FIGS. 4A and 4U, in some embodiments adjusting at leastone reactivity control rod having fast spectrum neutron absorbingmaterial, at least a portion of the neutron absorbing material includingfertile nuclear fission fuel material, responsive to the desiredreactivity parameter at the block 406 may include moving, in at leastone of two directions, at least one reactivity control rod having fastspectrum neutron absorbing material, at least a portion of the neutronabsorbing material including fertile nuclear fission fuel material,responsive to the desired reactivity parameter at a block 448. Invarious embodiments the directions may include axial directions in thenuclear fission reactor, radial directions in the nuclear fissionreactor, and/or lateral directions in the nuclear fission reactor.

Referring now to FIGS. 4A and 4V, in some embodiments sensing at leastone reactivity parameter at the block 428 may include sensing adifference in reactivity in association with a change in position of thereactivity control rod at a block 450.

Referring to FIGS. 4A and 4W, in some embodiments a sensor that isconfigured to sense at least one reactivity parameter may be calibratedat a block 452.

Referring now to FIG. 5A, a method 500 is provided for operating anuclear fission traveling wave reactor having a fast neutron spectrum.The method 500 starts at a block 502. At a block 503 a nuclear fissiontraveling wave having a fast neutron spectrum is propagated in a nuclearfission traveling wave reactor core. At a block 504 a desired reactivityparameter within a selected portion of the nuclear fission travelingwave reactor is determined. At a block 506 at least one reactivitycontrol rod having fast spectrum neutron absorbing material, at least aportion of the fast spectrum neutron absorbing material includingfertile nuclear fission fuel material, is adjusted responsive to thedesired reactivity parameter. The method 500 stops at a block 508.

Illustrative details will be set forth below by way of non-limitingexamples.

Referring now to FIGS. 5A and 5B, in some embodiments a nuclear fissiontraveling wave having a fast neutron spectrum may be initiated in thenuclear fission traveling wave reactor core at a block 509.

In various embodiments the desired reactivity parameter may bedetermined with respect to any portion of the nuclear fission travelingwave reactor as desired. For example and referring to FIG. 5C, in someembodiments determining a desired reactivity parameter within a selectedportion of the nuclear fission traveling wave reactor at the block 504may include determining at least one desired reactivity parameter of thefertile nuclear fission fuel material at a block 510. In some otherembodiments and referring to FIG. 5D, determining a desired reactivityparameter within a selected portion of the nuclear fission travelingwave reactor at the block 504 may include determining at least onedesired reactivity parameter of the at least one reactivity control rodat a block 512. In some other embodiments and referring to FIG. 5E,determining a desired reactivity parameter within a selected portion ofthe nuclear fission traveling wave reactor at the block 504 may includedetermining at least one desired reactivity parameter of the nuclearfission traveling wave reactor at a block 514.

In some embodiments the reactivity control rod may be adjustedresponsive to a difference between the desired reactivity parameter anda determination of the reactivity parameter. For example and referringto FIGS. 5A and 5F, in some embodiments at a block 516 at least onedetermined reactivity parameter may be determined. Referringadditionally to FIG. 5G, in some embodiments at a block 518 a differencebetween the desired reactivity parameter and the at least one determinedreactivity parameter may be determined. Referring additionally to FIG.5H, in some embodiments adjusting at least one reactivity control rodhaving fast spectrum neutron absorbing material, at least a portion ofthe neutron absorbing material including fertile nuclear fission fuelmaterial, responsive to the desired reactivity parameter at the block506 may include adjusting at least one reactivity control rod havingfast spectrum neutron absorbing material, at least a portion of theneutron absorbing material including fertile nuclear fission fuelmaterial, responsive to the difference between the desired reactivityparameter and the at least one determined reactivity parameter at ablock 520.

The determined reactivity parameter may be determined in any suitablemanner as desired. For example and referring now to FIGS. 5F and 5O, insome embodiments determining at least one determined reactivityparameter at the block 516 may include predicting at least onereactivity parameter at a block 522. Referring to FIGS. 5F and 5J, insome embodiments determining at least one determined reactivityparameter at the block 516 may include modeling at least one reactivityparameter at a block 524. Referring to FIGS. 5F and 5K, in someembodiments determining at least one determined reactivity parameter atthe block 516 may include selecting at least one predeterminedreactivity parameter at a block 526.

Referring to FIGS. 5F and 5L, in some other embodiments determining atleast one determined reactivity parameter at the block 516 may includesensing at least one reactivity parameter at a block 528. It will beappreciated that any desired reactivity parameter may be sensed at theblock 528 in any suitable manner.

For example and referring to FIGS. 5L and 5M, in some embodimentssensing at least one reactivity parameter at the block 528 may includesensing a time history of at least one reactivity parameter at a block530. Sensing a time history may be performed as desired, such as bysensing and recording or storing the sensed reactivity parameter morethan one time. Given by way of non-limiting examples, a time history ofat least one reactivity parameter may include, without limitation, arate of the reactivity parameter, accumulation of the reactivityparameter, total fissions, or the like. Referring to FIGS. 5L and 5N, insome embodiments sensing at least one reactivity parameter at the block528 may include sensing at least one radioactive decay event at a block532. Referring to FIGS. 5L and 5O, in some embodiments sensing at leastone reactivity parameter at the block 528 may include detecting fissionat a block 534. Referring to FIGS. 5L and 5P, in some embodimentssensing at least one reactivity parameter at the block 528 may includemonitoring neutron flux at a block 536. Referring to FIGS. 5L and 5Q, insome embodiments sensing at least one reactivity parameter at the block528 may include sensing neutron fluence at a block 538. Referring toFIGS. 5L and 5R, in some embodiments sensing at least one reactivityparameter at the block 528 may include detecting fission products at ablock 540.

Referring to FIGS. 5L and 5S, in some embodiments sensing at least onereactivity parameter at the block 528 may include sensing temperature ata block 542. Referring to FIGS. 5L and 5T, in some embodiments sensingat least one reactivity parameter at the block 528 may include sensingpressure at a block 544. Referring to FIGS. 5L and 5U, in someembodiments sensing at least one reactivity parameter at the block 528may include sensing power level at a block 546.

Referring now to FIGS. 5A and 5V, in some embodiments adjusting at leastone reactivity control rod having fast spectrum neutron absorbingmaterial, at least a portion of the neutron absorbing material includingfertile nuclear fission fuel material, responsive to the desiredreactivity parameter at the block 506 may include moving, in at leastone of two directions, at least one reactivity control rod having fastspectrum neutron absorbing material, at least a portion of the neutronabsorbing material including fertile nuclear fission fuel material,responsive to the desired reactivity parameter at a block 548. Invarious embodiments the directions may include axial directions in thenuclear fission traveling wave reactor, radial directions in the nuclearfission traveling wave reactor, and/or lateral directions in the nuclearfission traveling wave reactor.

Referring now to FIGS. 5A and 5W, in some embodiments sensing at leastone reactivity parameter at the block 528 may include sensing adifference in reactivity in association with a change in position of thereactivity control rod at a block 550.

Referring to FIGS. 5A and 5X, in some embodiments a sensor that isconfigured to sense at least one reactivity parameter may be calibratedat a block 552.

Referring now to FIG. 6A, an illustrative system 610 is provided forcontrolling reactivity in a nuclear fission reactor (not shown) having afast neutron spectrum. The system 610 includes means 612 for determininga desired reactivity parameter within a selected portion of a nuclearfission reactor having a fast neutron spectrum. The system 610 alsoincludes means 614 for adjusting at least one reactivity control rod(not shown) having fast spectrum neutron absorbing material, at least aportion of the fast spectrum neutron absorbing material includingfertile nuclear fission fuel material, responsive to the desiredreactivity parameter.

In various embodiments the determining means 612 may include suitableelectrical circuitry. As discussed above, various aspects describedherein (including the means 612 for determining a desired reactivityparameter within a selected portion of a nuclear fission reactor havinga fast neutron spectrum) can be implemented, individually and/orcollectively, by a wide range of hardware, software, firmware, or anycombination thereof that can be viewed as being composed of varioustypes of “electrical circuitry.” Consequently, it is emphasized that, asused herein “electrical circuitry” includes, but is not limited to,electrical circuitry having at least one discrete electrical circuit,electrical circuitry having at least one integrated circuit, electricalcircuitry having at least one application specific integrated circuit,electrical circuitry forming a general purpose computing deviceconfigured by a computer program (e.g., a general purpose computerconfigured by a computer program which at least partially carries outprocesses and/or devices described herein, or a microprocessorconfigured by a computer program which at least partially carries outprocesses and/or devices described herein), electrical circuitry forminga memory device (e.g., forms of random access memory), and/or electricalcircuitry forming a communications device (e.g., a modem, communicationsswitch, or optical-electrical equipment). Those having skill in the artwill recognize that the subject matter described herein may beimplemented in an analog or digital fashion or some combination thereof.

In various embodiments the adjusting means 614 may include any suitableelectro-mechanical system, such as without limitation an actuator. Givenby way of illustration and not limitation, a non-limiting example of anactuator includes a control rod drive mechanism. However, it will beappreciated that, in a general sense, the various embodiments describedherein can be implemented, individually and/or collectively, by varioustypes of electro-mechanical systems having a wide range of electricalcomponents such as hardware, software, firmware, or virtually anycombination thereof; and a wide range of components that may impartmechanical force or motion such as rigid bodies, spring or torsionalbodies, hydraulics, and electro-magnetically actuated devices, orvirtually any combination thereof. Consequently, as used herein“electro-mechanical system” includes, but is not limited to, electricalcircuitry operably coupled with a transducer (e.g., an actuator, amotor, a piezoelectric crystal, etc.), electrical circuitry having atleast one discrete electrical circuit, electrical circuitry having atleast one integrated circuit, electrical circuitry having at least oneapplication specific integrated circuit, electrical circuitry forming ageneral purpose computing device configured by a computer program (e.g.,a general purpose computer configured by a computer program which atleast partially carries out processes and/or devices described herein,or a microprocessor configured by a computer program which at leastpartially carries out processes and/or devices described herein),electrical circuitry forming a memory device (e.g., forms of randomaccess memory), electrical circuitry forming a communications device(e.g., a modem, communications switch, or optical-electrical equipment),and any non-electrical analog thereto, such as optical or other analogs.Those skilled in the art will also appreciate that examples ofelectro-mechanical systems include but are not limited to a variety ofconsumer electronics systems, as well as other systems such as motorizedtransport systems, factory automation systems, security systems, andcommunication/computing systems. Those skilled in the art will recognizethat electro-mechanical as used herein is not necessarily limited to asystem that has both electrical and mechanical actuation except ascontext may dictate otherwise.

In some embodiments the fast spectrum neutrons may be part of a nuclearfission traveling wave. In such cases, the nuclear fission reactor mayinclude a nuclear fission traveling wave reactor. However, it will beappreciated that in other embodiments the fast spectrum neutrons neednot be part of a nuclear fission traveling wave. Thus, in someembodiments, the nuclear fission reactor may include any suitablenuclear fission reactor having a fast neutron spectrum.

Referring to FIG. 6B, in some embodiments the means 612 for determininga desired reactivity parameter may include means 616 for determining atleast one desired reactivity parameter of the fertile nuclear fissionfuel material. In some other embodiments and referring to FIG. 6C, themeans 612 for determining a desired reactivity parameter may includemeans 618 for determining at least one desired reactivity parameter ofthe at least one reactivity control rod. In some other embodiments andreferring to FIG. 6D, the means 612 for determining a desired reactivityparameter may include means 620 for determining at least one desiredreactivity parameter of the nuclear fission reactor. The means 616, 618,and 620 may include suitable electrical circuitry, as described above.

Referring now to FIG. 6E, in some embodiments the system 610 may alsoinclude means 622 for determining at least one determined reactivityparameter. In some embodiments the means 622 may include suitableelectrical circuitry, as described above. Some other embodiments of themeans 622 will be discussed below.

Referring now to FIG. 6F, in some embodiments the system 610 may alsoinclude means 624 for determining a difference between the desiredreactivity parameter and the at least one determined reactivityparameter. The means 624 may include suitable electrical circuitry, asdescribed above, such as without limitation a comparator.

Referring additionally to FIG. 6G, in some embodiments the adjustingmeans 614 may include means 626 for adjusting at least one reactivitycontrol rod having fast spectrum neutron absorbing material, at least aportion of the fast spectrum neutron absorbing material includingfertile nuclear fission fuel material, responsive to the differencebetween the desired reactivity parameter and the at least one determinedreactivity parameter. The means 626 may include any suitableelectro-mechanical system as described above, such as without limitationa control rod drive mechanism.

In various embodiments the determining means 622 may determine adetermined reactivity parameter in any manner as desired for aparticular application. For example and referring to FIG. 6H, in someembodiments the means 622 for determining at least one determinedreactivity parameter may include means 628 for predicting at least onereactivity parameter. The means 628 may include suitable electricalcircuitry, as described above. Given by way of non-limiting example, thepredetermined reactivity parameter may be retrieved from a look-up tableusing operating parameters, such as temperature, pressure, power level,time in core life (as measured in effective full power hours), and thelike, as entering arguments.

Referring to FIG. 6I, in some other embodiments the means 622 fordetermining at least one determined reactivity parameter may includemeans 630 for modeling at least one reactivity parameter. The means 630may include suitable electrical circuitry, as described above, such aswithout limitation a suitable computer. The means 630 may also includesuitable neutronics modeling software that runs on the electricalcircuitry. Given by way of illustration, suitable neutronics modelingsoftware includes MCNP, CINDER, REBUS, and the like.

Referring to FIG. 6J, in some embodiments the means 622 for determiningat least one determined reactivity parameter may include means 632 forselecting at least one predetermined reactivity parameter. The means 632may include suitable electrical circuitry, as described above.

Referring to FIG. 6K, in some embodiments the means 622 for determiningat least one determined reactivity parameter may include means 634 forsensing at least one reactivity parameter. In various embodiments, thesensing means 634 may include any one or more of various sensors anddetectors as desired for a particular purpose, as will be discussedbelow.

Referring to FIG. 6L, in some embodiments the sensing means 634 mayinclude means 636 for sensing a time history of at least one reactivityparameter. Sensing a time history may be performed as desired, such asby sensing and recording or storing the sensed reactivity parameter morethan one time. Given by way of non-limiting examples, a time history ofat least one reactivity parameter may include, without limitation, arate of the reactivity parameter, accumulation of the reactivityparameter, total fissions, or the like. In various embodiments the means636 may include suitable storage, such as computer memory media orcomputer memory storage or the like, configured to store values of thereactivity parameter over time.

Referring to FIG. 6M, in some other embodiments the sensing means 634may include 638 means for sensing at least one radioactive decay event.Given by way of non-limiting examples, the means 638 may include any oneor more of suitable sensors or detectors for sensing α, β, and/or γradiation as desired.

Referring back to FIG. 6K, in various embodiments the sensing means 634may include any suitable sensor as desired for a particular application.Given by way of illustrative examples and without limitation, in variousembodiments the sensing means 634 may include any one or more sensor,such as at least one fission detector, a neutron flux monitor, a neutronfluence sensor, a fission product detector, a temperature sensor, apressure sensor, and/or a power level sensor.

Referring to FIG. 6N, in some embodiments the adjusting means 614 mayinclude means 640 for moving, in at least one of two directions, atleast one reactivity control rod having fast spectrum neutron absorbingmaterial, at least a portion of the fast spectrum neutron absorbingmaterial including fertile nuclear fission fuel material, responsive tothe desired reactivity parameter. In some embodiments, the means 640 mayinclude an actuator such as a control rod drive mechanism and/or a rodhandling system. In various embodiments, the directions may include anyone or more of axial directions in the nuclear fission reactor, radialdirections in the nuclear fission reactor, and/or lateral directions inthe nuclear fission reactor.

Referring to FIG. 6O, in some embodiments the sensing means 634 mayinclude means 642 for sensing a difference in reactivity in associationwith a change in position of the reactivity control rod. In variousembodiments, the means 642 may include electrical circuitry, asdescribed above. In some embodiments the electrical circuitry mayimplement a suitable comparator.

Referring to FIG. 6P, in some embodiments the system 610 may alsoinclude means 644 for calibrating the sensing means 634. In variousembodiments the calibration means 644 suitably includes a source havingknown characteristics or attributes of the reactivity parameter,discussed above, that is sensed by the sensing means 634.

Referring now to FIG. 7A, a method 700 is provided for determining anapplication of a controllably movable rod. The method 700 starts at ablock 702. At a block 704 at least one reactivity parameter of acontrollably movable rod in a nuclear fission reactor is determined, thecontrollably movable rod including fertile nuclear fission fuelmaterial. At a block 706 an application of the controllably movable rod,chosen from a reactivity control rod and a nuclear fission fuel rod, isdetermined. The method 700 stops at a block 708.

In various embodiments, the application of the controllably movable rod(chosen from a reactivity control rod and a nuclear fission fuel rod)may be determined responsive to the at least one determined reactivityparameter in the controllably movable rod. Non limiting examples givenby way of illustration and not of limitation will be described below.

Referring to FIG. 7B, in some embodiments at a block 710 the determinedreactivity parameter and a target reactivity parameter may be compared.In some embodiments, an application of the controllably movable rod(chosen from a reactivity control rod and a nuclear fission fuel rod)may be determined responsive to comparison of the determined reactivityparameter and the target reactivity parameter.

Referring back to FIG. 7A, in some embodiments the at least onereactivity parameter may include a neutron absorption coefficient.Referring to FIG. 7C, in some embodiments at a block 712 the determinedneutron absorption coefficient a target neutron absorption coefficientmay be compared. In some embodiments, an application of the controllablymovable rod (chosen from a reactivity control rod and a nuclear fissionfuel rod) may be determined responsive to comparison of the determinedneutron absorption coefficient and the target neutron absorptioncoefficient. For example, a chosen application of the controllablymovable rod may include a reactivity control rod when the determinedneutron absorption coefficient is at least the target neutron absorptioncoefficient. As another example, a chosen application of thecontrollably movable rod may include a nuclear fission fuel rod when thedetermined neutron absorption coefficient is less than the targetneutron absorption coefficient.

Referring back to FIG. 7A, in some other embodiments the at least onereactivity parameter may include a neutron production coefficient.Referring to FIG. 7D, in some embodiments at a block 714 the determinedneutron production coefficient and a target neutron productioncoefficient may be compared. In some embodiments, an application of thecontrollably movable rod (chosen from a reactivity control rod and anuclear fission fuel rod) may be determined responsive to comparison ofthe determined neutron production coefficient and the target neutronproduction coefficient. For example, a chosen application of thecontrollably movable rod may include a nuclear fission fuel rod when thedetermined neutron production coefficient is at least the target neutronproduction coefficient. As another example, a chosen application of thecontrollably movable rod may include a reactivity control rod when thedetermined neutron production coefficient is less than the targetneutron production coefficient.

Referring back to FIG. 7A, the at least one reactivity parameter may bedetermined in any manner as desired for a particular application. Givenby way of non-limiting examples, determining at least one reactivityparameter of a controllably movable rod in a nuclear fission reactor maybe based on neutron exposure history of the controllably movable rod, aproperty of fertile nuclear fission fuel material of the controllablymovable rod, a property of fissile nuclear fission fuel material of thecontrollably movable rod, a property of neutron absorbing poison of thecontrollably movable rod, and/or a property of fission products of thecontrollably movable rod.

Referring to FIG. 7E, in some embodiments determining at least onereactivity parameter of a controllably movable rod in a nuclear fissionreactor at the block 704 may include monitoring at least one reactivityparameter of a controllably movable rod in a nuclear fission reactor ata block 716.

Referring to FIG. 7F, in some other embodiments determining at least onereactivity parameter of a controllably movable rod in a nuclear fissionreactor at the block 704 may include predicting at least one reactivityparameter of a controllably movable rod in a nuclear fission reactor ata block 718. Referring to FIG. 7G, in some embodiments predicting atleast one reactivity parameter of a controllably movable rod in anuclear fission reactor at the block 718 may include calculating atleast one reactivity parameter of a controllably movable rod in anuclear fission reactor at a block 720.

Referring now to FIG. 8A, a system 810 is provided for determining anapplication of a controllably movable rod. An apparatus 812 isconfigured to determine at least one reactivity parameter of acontrollably movable rod in a nuclear fission reactor, the controllablymovable rod including fertile nuclear fission fuel material. Electricalcircuitry 814 is configured to determine an application of thecontrollably movable rod chosen from a reactivity control rod and anuclear fission fuel rod.

In various embodiments, the application of the controllably movable rod(chosen from a reactivity control rod and a nuclear fission fuel rod)may be determined responsive to the at least one determined reactivityparameter in the controllably movable rod. Non limiting examples givenby way of illustration and not of limitation will be described below.

Referring to FIG. 8B, a comparator 816 may be configured to compare thedetermined reactivity parameter and a target reactivity parameter. Insuch a case, the electrical circuitry 814 may be responsive to thecomparator 816.

Still referring to FIG. 8B, in some embodiments the at least onereactivity parameter may include a neutron absorption coefficient. Insuch cases, the comparator 816 may be further configured to compare thedetermined neutron absorption coefficient with a target neutronabsorption coefficient. The electrical circuitry 814 may be responsiveto comparison of the determined neutron absorption coefficient and thetarget neutron absorption coefficient by the comparator 816. In someembodiments a chosen application of the controllably movable rod mayinclude a reactivity control rod when the determined neutron absorptioncoefficient is at least the target neutron absorption coefficient. Insome other embodiments a chosen application of the controllably movablerod may include a nuclear fission fuel rod when the determined neutronabsorption coefficient is less than the target neutron absorptioncoefficient.

Still referring to FIG. 8B, in some other embodiments the at least onereactivity parameter may include a neutron production coefficient. Insuch cases, the comparator 816 may be further configured to compare thedetermined neutron production coefficient with a target neutronproduction coefficient. The electrical circuitry 814 may be responsiveto comparison of the determined neutron production coefficient and thetarget neutron production coefficient by the comparator 816. In someembodiments a chosen application of the controllably movable rod mayinclude a nuclear fission fuel rod when the determined neutronproduction coefficient is at least the target neutron productioncoefficient. In some other embodiments a chosen application of thecontrollably movable rod may include a reactivity control rod when thedetermined neutron production coefficient is less than the targetneutron production coefficient.

Referring back to FIG. 8A, in various embodiments the apparatus 812 maybe configured as desired to determine the reactivity parameter. Forexample and referring to FIG. 8C, in some embodiments the apparatus 812may include electrical circuitry 818 that is configured to determine atleast one reactivity parameter of a controllably movable rod in anuclear fission reactor based on neutron exposure history of thecontrollably movable rod.

Referring to FIG. 8D, in some other embodiments the apparatus 812 mayinclude electrical circuitry 820 that is configured to determine atleast one reactivity parameter of a controllably movable rod in anuclear fission reactor based on a property of fertile nuclear fissionfuel material of the controllably movable rod. Referring to FIG. 8E, insome embodiments the apparatus 812 may include electrical circuitry 822that is configured to determine at least one reactivity parameter of acontrollably movable rod in a nuclear fission reactor based on aproperty of fissile nuclear fission fuel material of the controllablymovable rod.

Referring to FIG. 8F, in some embodiments the apparatus 812 may includeelectrical circuitry 824 that is configured to determine at least onereactivity parameter of a controllably movable rod in a nuclear fissionreactor based on a property of neutron absorbing poison of thecontrollably movable rod. Referring to FIG. 8G, in some embodiments theapparatus 812 may include electrical circuitry 826 that is configured todetermine at least one reactivity parameter of a controllably movablerod in a nuclear fission reactor based on a property of fission productsof the controllably movable rod.

Referring to FIG. 8H, in some embodiments the apparatus 812 may includeat least one monitoring device 828 that is configured to monitor atleast one reactivity parameter of a controllably movable rod in anuclear fission reactor. Given by way of non-limiting examples, themonitoring device 828 may include any one or more of the sensors and/ordetectors described above.

Referring to FIG. 8I, in some embodiments the apparatus 812 may includeelectrical circuitry 830 that is configured to predict at least onereactivity parameter of a controllably movable rod in a nuclear fissionreactor. For example, in some embodiments the electrical circuitry 830may be further configured to calculate at least one reactivity parameterof a controllably movable rod in a nuclear fission reactor.

Referring to FIG. 9A, an illustrative method 900 is provided foroperating a nuclear fission traveling wave reactor. The method 900starts at a block 902. At a block 904 a reactivity control apparatushaving a first worth is inserted into a first location of a reactor coreof a nuclear fission traveling wave reactor. At a block 906, worth ofthe reactivity control apparatus is modified. At a block 908 thereactivity control apparatus is moved from the first location to asecond location of the reactor core of the nuclear fission travelingwave reactor such that the reactivity control apparatus has a secondworth that is different from the first worth. The method 900 stops at ablock 910.

Referring to FIG. 9B, in some embodiments modifying worth of thereactivity control apparatus at the block 906 may include absorbingneutrons by the reactivity control apparatus at a block 912. Referringto FIG. 9C, in some embodiments, absorbing neutrons by the reactivitycontrol apparatus at the block 912 may include absorbing neutrons byfertile nuclear fission fuel material of the reactivity controlapparatus at a block 914. In some of the cases, the second worth may begreater than the first worth.

Referring to FIG. 9D, in some other embodiments modifying worth of thereactivity control apparatus at the block 906 may include modifyingabsorptive effect of self-shielded burnable poison of the reactivitycontrol rod at a block 916. Referring to FIG. 9E, in some embodimentsmodifying absorptive effect of self-shielded burnable poison of thereactivity control rod at the block 916 may include modifyingself-shielding effect of the self-shielded burnable poison at a block918. Referring to FIG. 9F, in some embodiments modifying self-shieldingeffect of the self-shielded burnable poison at the block 918 may includemodifying exposure of the self-shielded burnable poison to a neutronflux at a block 920. Referring to FIG. 9G, in some embodiments modifyingexposure of the self-shielded burnable poison to a neutron flux at theblock 920 may include modifying neutron energy at a block 922. In someembodiments the second worth may be less than the first worth. In someother embodiments the second worth may be greater than the first worth.

In a general sense, those skilled in the art will recognize that thevarious embodiments described herein can be implemented, individuallyand/or collectively, by various types of electro-mechanical systemshaving a wide range of electrical components such as hardware, software,firmware, or virtually any combination thereof; and a wide range ofcomponents that may impart mechanical force or motion such as rigidbodies, spring or torsional bodies, hydraulics, and electro-magneticallyactuated devices, or virtually any combination thereof. Consequently, asused herein “electro-mechanical system” includes, but is not limited to,electrical circuitry operably coupled with a transducer (e.g., anactuator, a motor, a piezoelectric crystal, etc.), electrical circuitryhaving at least one discrete electrical circuit, electrical circuitryhaving at least one integrated circuit, electrical circuitry having atleast one application specific integrated circuit, electrical circuitryforming a general purpose computing device configured by a computerprogram (e.g., a general purpose computer configured by a computerprogram which at least partially carries out processes and/or devicesdescribed herein, or a microprocessor configured by a computer programwhich at least partially carries out processes and/or devices describedherein), electrical circuitry forming a memory device (e.g., forms ofrandom access memory), electrical circuitry forming a communicationsdevice (e.g., a modem, communications switch, or optical-electricalequipment), and any non-electrical analog thereto, such as optical orother analogs. Those skilled in the art will also appreciate thatexamples of electro-mechanical systems include but are not limited to avariety of consumer electronics systems, as well as other systems suchas motorized transport systems, factory automation systems, securitysystems, and communication/computing systems. Those skilled in the artwill recognize that electro-mechanical as used herein is not necessarilylimited to a system that has both electrical and mechanical actuationexcept as context may dictate otherwise.

In a general sense, those skilled in the art will recognize that thevarious aspects described herein which can be implemented, individuallyand/or collectively, by a wide range of hardware, software, firmware, orany combination thereof can be viewed as being composed of various typesof “electrical circuitry.” Consequently, as used herein “electricalcircuitry” includes, but is not limited to, electrical circuitry havingat least one discrete electrical circuit, electrical circuitry having atleast one integrated circuit, electrical circuitry having at least oneapplication specific integrated circuit, electrical circuitry forming ageneral purpose computing device configured by a computer program (e.g.,a general purpose computer configured by a computer program which atleast partially carries out processes and/or devices described herein,or a microprocessor configured by a computer program which at leastpartially carries out processes and/or devices described herein),electrical circuitry forming a memory device (e.g., forms of randomaccess memory), and/or electrical circuitry forming a communicationsdevice (e.g., a modem, communications switch, or optical-electricalequipment). Those having skill in the art will recognize that thesubject matter described herein may be implemented in an analog ordigital fashion or some combination thereof.

Those having skill in the art will recognize that the state of the arthas progressed to the point where there is little distinction leftbetween hardware and software implementations of aspects of systems; theuse of hardware or software is generally (but not always, in that incertain contexts the choice between hardware and software can becomesignificant) a design choice representing cost vs. efficiency tradeoffs.Those having skill in the art will appreciate that there are variousvehicles by which processes and/or systems and/or other technologiesdescribed herein can be effected (e.g., hardware, software, and/orfirmware), and that the preferred vehicle will vary with the context inwhich the processes and/or systems and/or other technologies aredeployed. For example, if an implementer determines that speed andaccuracy are paramount, the implementer may opt for a mainly hardwareand/or firmware vehicle; alternatively, if flexibility is paramount, theimplementer may opt for a mainly software implementation; or, yet againalternatively, the implementer may opt for some combination of hardware,software, and/or firmware. Hence, there are several possible vehicles bywhich the processes and/or devices and/or other technologies describedherein may be effected, none of which is inherently superior to theother in that any vehicle to be utilized is a choice dependent upon thecontext in which the vehicle will be deployed and the specific concerns(e.g., speed, flexibility, or predictability) of the implementer, any ofwhich may vary. Those skilled in the art will recognize that opticalaspects of implementations will typically employ optically-orientedhardware, software, and or firmware.

The foregoing detailed description has set forth various embodiments ofthe devices and/or processes via the use of block diagrams, flowcharts,and/or examples. Insofar as such block diagrams, flowcharts, and/orexamples contain one or more functions and/or operations, it will beunderstood by those within the art that each function and/or operationwithin such block diagrams, flowcharts, or examples can be implemented,individually and/or collectively, by a wide range of hardware, software,firmware, or virtually any combination thereof. In one embodiment,several portions of the subject matter described herein may beimplemented via Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs), digital signal processors (DSPs), orother integrated formats. However, those skilled in the art willrecognize that some aspects of the embodiments disclosed herein, inwhole or in part, can be equivalently implemented in integratedcircuits, as one or more computer programs running on one or morecomputers (e.g., as one or more programs running on one or more computersystems), as one or more programs running on one or more processors(e.g., as one or more programs running on one or more microprocessors),as firmware, or as virtually any combination thereof, and that designingthe circuitry and/or writing the code for the software and or firmwarewould be well within the skill of one of skill in the art in light ofthis disclosure. In addition, those skilled in the art will appreciatethat the mechanisms of the subject matter described herein are capableof being distributed as a program product in a variety of forms, andthat an illustrative embodiment of the subject matter described hereinapplies regardless of the particular type of signal bearing medium usedto actually carry out the distribution. Examples of a signal bearingmedium include, but are not limited to, the following: a recordable typemedium such as a floppy disk, a hard disk drive, a Compact Disc (CD), aDigital Video Disk (DVD), a digital tape, a computer memory, etc.; and atransmission type medium such as a digital and/or an analogcommunication medium (e.g., a fiber optic cable, a waveguide, a wiredcommunications link, a wireless communication link, etc.).

It will be appreciated that each block of block diagrams and flowcharts,and combinations of blocks in block diagrams and flowcharts, can beimplemented by computer program instructions. These computer programinstructions may be loaded onto a computer or other programmableapparatus to produce a machine, such that the instructions which executeon the computer or other programmable apparatus create computer-readablemedia software program code configured to implement the functionsspecified in the block diagram or flowchart block(s). These computerprogram instructions may also be stored in a computer-readable memorythat can direct a computer or other programmable apparatus to functionin a particular manner, such that the instructions stored in thecomputer-readable memory produce an article of manufacture includingcomputer-readable media software program code instructions whichimplement the function specified in the block diagram or flowchartblock(s). The computer-readable media software program code instructionsmay also be loaded onto a computer or other programmable apparatus tocause a series of operational steps to be performed on the computer orother programmable apparatus to produce a computer implemented processsuch that the instructions which execute on the computer or otherprogrammable apparatus provide steps for implementing the functionsspecified in the block diagram or flowchart block(s).

Accordingly, blocks of the block diagrams or flowcharts supportcombinations of means for performing the specified functions,combinations of steps for performing the specified functions, andcomputer-readable media software program code for performing thespecified functions. It will also be understood that each block of theblock diagrams or flowcharts, and combinations of blocks in the blockdiagrams or flowcharts, can be implemented by special purposehardware-based computer systems which perform the specified functions orsteps, or combinations of special purpose hardware and computerinstructions.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations are not expressly set forth herein for sakeof clarity.

The herein described subject matter sometimes illustrates differentcomponents contained within, or connected with, different othercomponents. It is to be understood that such depicted architectures aremerely exemplary, and that in fact many other architectures can beimplemented which achieve the same functionality. In a conceptual sense,any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality can be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermedial components. Likewise, any two components soassociated can also be viewed as being “operably connected”, or“operably coupled”, to each other to achieve the desired functionality,and any two components capable of being so associated can also be viewedas being “operably couplable”, to each other to achieve the desiredfunctionality. Specific examples of operably couplable include but arenot limited to physically mateable and/or physically interactingcomponents and/or wirelessly interactable and/or wirelessly interactingcomponents and/or logically interacting and/or logically interactablecomponents.

In some instances, one or more components may be referred to herein as“configured to.” Those skilled in the art will recognize that“configured to” can generally encompass active-state components and/orinactive-state components and/or standby-state components, etc. unlesscontext requires otherwise.

In some instances, one or more components may be referred to herein as“configured to.” Those skilled in the art will recognize that“configured to” can generally encompass active-state components and/orinactive-state components and/or standby-state components, unlesscontext requires otherwise.

While particular aspects of the present subject matter described hereinhave been shown and described, it will be apparent to those skilled inthe art that, based upon the teachings herein, changes and modificationsmay be made without departing from the subject matter described hereinand its broader aspects and, therefore, the appended claims are toencompass within their scope all such changes and modifications as arewithin the true spirit and scope of the subject matter described herein.Furthermore, it is to be understood that the invention is defined by theappended claims. It will be understood by those within the art that, ingeneral, terms used herein, and especially in the appended claims (e.g.,bodies of the appended claims) are generally intended as “open” terms(e.g., the term “including” should be interpreted as “including but notlimited to,” the term “having” should be interpreted as “having atleast,” the term “includes” should be interpreted as “includes but isnot limited to,” etc.). It will be further understood by those withinthe art that if a specific number of an introduced claim recitation isintended, such an intent will be explicitly recited in the claim, and inthe absence of such recitation no such intent is present. For example,as an aid to understanding, the following appended claims may containusage of the introductory phrases “at least one” and “one or more” tointroduce claim recitations. However, the use of such phrases should notbe construed to imply that the introduction of a claim recitation by theindefinite articles “a” or “an” limits any particular claim containingsuch introduced claim recitation to inventions containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should typically be interpreted to mean “atleast one” or “one or more”); the same holds true for the use ofdefinite articles used to introduce claim recitations. In addition, evenif a specific number of an introduced claim recitation is explicitlyrecited, those skilled in the art will recognize that such recitationshould typically be interpreted to mean at least the recited number(e.g., the bare recitation of “two recitations,” without othermodifiers, typically means at least two recitations, or two or morerecitations). Furthermore, in those instances where a conventionanalogous to “at least one of A, B, and C, etc.” is used, in generalsuch a construction is intended in the sense one having skill in the artwould understand the convention (e.g., “a system having at least one ofA, B, and C” would include but not be limited to systems that have Aalone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). In those instances where aconvention analogous to “at least one of A, B, or C, etc.” is used, ingeneral such a construction is intended in the sense one having skill inthe art would understand the convention (e.g., “a system having at leastone of A, B, or C” would include but not be limited to systems that haveA alone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). It will be furtherunderstood by those within the art that virtually any disjunctive wordand/or phrase presenting two or more alternative terms, whether in thedescription, claims, or drawings, should be understood to contemplatethe possibilities of including one of the terms, either of the terms, orboth terms. For example, the phrase “A or B” will be understood toinclude the possibilities of “A” or “B” or “A and B.”

With respect to the appended claims, those skilled in the art willappreciate that recited operations therein may generally be performed inany order. Examples of such alternate orderings may include overlapping,interleaved, interrupted, reordered, incremental, preparatory,supplemental, simultaneous, reverse, or other variant orderings, unlesscontext dictates otherwise. With respect to context, even terms like“responsive to,” “related to,” or other past-tense adjectives aregenerally not intended to exclude such variants, unless context dictatesotherwise.

Those skilled in the art will appreciate that the foregoing specificillustrative processes and/or devices and/or technologies arerepresentative of more general processes and/or devices and/ortechnologies taught elsewhere herein, such as in the claims filedherewith and/or elsewhere in the present application.

One skilled in the art will recognize that the herein describedcomponents (e.g., process blocks), devices, and objects and thediscussion accompanying them are used as examples for the sake ofconceptual clarity and that various configuration modifications arewithin the skill of those in the art. Consequently, as used herein, thespecific examples set forth and the accompanying discussion are intendedto be representative of their more general classes. In general, use ofany specific example herein is also intended to be representative of itsclass, and the non-inclusion of such specific components (e.g., processblocks), devices, and objects herein should not be taken as indicatingthat limitation is desired.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

The invention claimed is:
 1. A method of controlling reactivity in anuclear fission reactor having a fast neutron spectrum, the methodcomprising: determining a desired reactivity parameter within a selectedportion of a nuclear fission reactor having a fast neutron spectrum; andadjusting at least one reactivity control rod having fast spectrumneutron absorbing material, at least a portion of the fast spectrumneutron absorbing material including fertile nuclear fission fuelmaterial, responsive to the desired reactivity parameter.
 2. The methodof claim 1, wherein the fast spectrum neutrons are part of a nuclearfission traveling wave.
 3. The method of claim 1, wherein determining adesired reactivity parameter within a selected portion of a nuclearfission reactor having a fast neutron spectrum includes determining atleast one desired reactivity parameter of the fertile nuclear fissionfuel material.
 4. The method of claim 1, wherein determining a desiredreactivity parameter within a selected portion of a nuclear fissionreactor having a fast neutron spectrum includes determining at least onedesired reactivity parameter of the at least one reactivity control rod.5. The method of claim 1, wherein determining a desired reactivityparameter within a selected portion of a nuclear fission reactor havinga fast neutron spectrum includes determining at least one desiredreactivity parameter of the nuclear fission reactor.
 6. The method ofclaim 1, further comprising determining at least one determinedreactivity parameter.
 7. The method of claim 6, further comprisingdetermining a difference between the desired reactivity parameter andthe at least one determined reactivity parameter.
 8. The method of claim7, wherein adjusting at least one reactivity control rod having fastspectrum neutron absorbing material, at least a portion of the neutronabsorbing material including fertile nuclear fission fuel material,responsive to the desired reactivity parameter includes adjusting atleast one reactivity control rod having fast spectrum neutron absorbingmaterial, at least a portion of the neutron absorbing material includingfertile nuclear fission fuel material, responsive to the differencebetween the desired reactivity parameter and the at least one determinedreactivity parameter.
 9. The method of claim 6, wherein determining atleast one determined reactivity parameter includes predicting at leastone reactivity parameter.
 10. The method of claim 6, wherein determiningat least one determined reactivity parameter includes modeling at leastone reactivity parameter.
 11. The method of claim 6, wherein determiningat least one determined reactivity parameter includes selecting at leastone predetermined reactivity parameter.
 12. The method of claim 6,wherein determining at least one determined reactivity parameterincludes sensing at least one reactivity parameter.
 13. The method ofclaim 12, wherein sensing at least one reactivity parameter includessensing a time history of at least one reactivity parameter.
 14. Themethod of claim 12, wherein sensing at least one reactivity parameterincludes sensing at least one parameter chosen from a radioactive decayevent, fission, neutron flux, neutron fluence, fission products,temperature, pressure, and power level.
 15. The method of claim 1,wherein adjusting at least one reactivity control rod having fastspectrum neutron absorbing material, at least a portion of the neutronabsorbing material including fertile nuclear fission fuel material,responsive to the desired reactivity parameter includes moving, in atleast one of two directions, at least one reactivity control rod havingfast spectrum neutron absorbing material, at least a portion of theneutron absorbing material including fertile nuclear fission fuelmaterial, responsive to the desired reactivity parameter.
 16. The methodof claim 15, wherein the directions include directions chosen from axialdirections in the nuclear fission reactor, radial directions in thenuclear fission reactor, and lateral directions in the nuclear fissionreactor.
 17. The method of claim 12, wherein sensing at least onereactivity parameter includes sensing a difference in reactivity inassociation with a change in position of the reactivity control rod. 18.The method of claim 12, further comprising calibrating a sensorconfigured to sense at least one reactivity parameter.